Gold in the silver screen?

The adaptation of Irvine Welsh's Filth is one of three such films that will be in cinemas by Friday. It will be competing for audiences with Sunshine On Leith, based on the music of The Proclaimers, and Last King of Scotland director Kevin Macdonald's How I Live Now, set in a post-apocalyptic world.

Meanwhile, Scottish ­director Paul Wright's debut For Those in Peril, about tragedy in a fishing village, will be screened in cinemas in England on Friday, ahead of opening in Scotland on November 8.

Scottish-made Under The Skin, starring Scarlett Johansson; The Railway Man, with Colin Firth, which was filmed in Scotland; and Scots director David Mackenzie's Starred Up are due out next year.

All this follows the high-profile World War Z, which saw Brad Pitt and his crew descend on Glasgow last year, and the starring role of the Highlands in Skyfall, which became the top UK box office hit of 2012.

Yet some of Scotland's leading independent film producers say all this activity distorts a picture that is in reality ''extremely bleak''.

Their warning comes in a memo sent by the Independent Producers Scotland group to national arts body Creative Scotland. Among those who have signed the letter is Gillian Berrie, founder of Film City Glasgow and Sigma Films.

She told the Sunday Herald she was delighted to see so many ­Scottish films coming out at the same time, but argued a lack of investment, dedicated screen agency and long-term film strategy has left the country lagging behind.

"Eight years ago, I would have said we were 10 years ahead of our neighbouring countries, some of the smaller ones such as Northern Ireland - now they are 10 years ahead of us," she said.

"Ten years ago they [Northern Ireland] sat down and came up with a long-term strategy for growth. They knew they were going to have to invest a lot of money - they knew they would have to have a fully operating sound stage studio, they created that and, lo and behold, their £15 million investment is now repaying a £90m return."

Berrie, who co-produced Under the Skin, said: "Although it all looks lovely on the surface because these films are coming out, underneath you have not very many Scottish producers left that want to stay here and make films as it is just too hard. It is brutal."

Berrie stressed that ­competition in the industry is fierce internationally, with every £1 invested bringing a return of £9. "On the paltry £3m we have at the moment, look at what film has achieved. What if we had £30m?" she asks.

Robin MacPherson, professor of screen media at Napier University, said the film industry in Scotland was enjoying a crescendo that "only happens once in a while".

"We have to be cautious in terms of interpreting that as a boom, in that there are a lot more films being made, which isn't the case. It helps people and ­producers and talent to get attention, but it doesn't change the underlying need to get more investment and more projects made at different scales to increase our chances of sustaining that success."

Lorne Boswell, national official for Scotland and Northern Ireland at Equity, said the film and television industry was too "London-centric".

"The frustration from the actor's point of view is that not enough is cast up here," he said.

"We understand that to get a project together you are going to need your headline names, and there is an international market for that, but there is absolutely no reason why once that is in place, a lot of the rest of the stuff isn't cast up here."

Scotland has also received a major boost in the form of the arrival of the television series Outlander, which is being filmed for major US cable network Starz in a studio in Cumbernauld, North Lanarkshire.

It has been hailed as a potential game-changer for the industry, with the £20m that will be spent filming the time-travelling adventure series said to be the biggest single inward investment through film and television for Scotland.

Boswell added: "I think there are signs of improvement, and hopefully Outlander will create jobs. Game Of Thrones has done a lot for Northern Ireland, so I think there are grounds to be optimistic."

The real potential game-changer for the industry would be a dedicated film studio north of the Border, which has long been mooted but never come to fruition.

A task force was set up by the Scottish Government in May to examine the idea. Initial findings are due in the next couple of weeks.

Glasgow-based director Zam Salim, who has just been nominated for a "Breakthrough Brit" Bafta award, said having a studio was a business essential, but pointed out time would also have to be spent nurturing filmmakers.

"It is a tricky proposition to develop a film culture but I think you need to give opportunities or help people who just really want to make a film," he said.

"As soon as you have a little bit of success, people jump on this slightly hysterical idea that 'we are on a roll'.

"Anyone who knows how film works knows that it doesn't have that kind of momentum to it, but then everyone gets really disappointed.''

However, Caroline Parkinson, director of creative development at Creative Scotland, believes the industry in Scotland is "on the cusp of something".

She said the release of so many Scottish films had been helped by behind-the-scenes work by the agency, such as actively marketing locations and brokering meetings between Scottish producers and studios and distributors.

"I would say there is a cohesion here around the current generation of filmmakers," she said. "They have got some energy, dynamism and they really want to go for it."

Outlander, she said, would help certainly boost confidence in the industry. "It will hire crew and heads of department and it will lift people up who have been on the verge of those roles."

But it's not just about the industry. A much-touted benefit of having Scotland appear on the big screen is the boost it brings to tourism.

One in five visitors to ­Scotland is influenced by seeing the country in films and on ­television, according to national tourism agency VisitScotland. To capitalise on an expected surge in interest from Sunshine On Leith, it has produced a movie map of the Edinburgh locations featured in the film.

By far the biggest film project to date for VisitScotland was working with Disney to boost marketing in the wake of the 2012 animated movie Brave. The agency's research estimates £120m will be spent in Scotland over the next five years by visitors who have seen the film.

Professor John Lennon, director of the Moffat Centre for Development at Glasgow Caledonian University, pointed out it was difficult to pinpoint a clear link between someone seeing Sunshine On Leith, for example, and then visiting Scotland.

But he added: "If you have a lot of movies featuring Scotland and many of them featuring it in quite a positive way, then you will get spin-off undoubtedly. It is just another way of a nation presenting itself to an international audience."

A spokeswoman for the ­Scottish Government said: "Through Creative Scotland, we are doing much to support the film and television industry in Scotland, supporting the local industry as well as attracting international productions.

"Scotland has the capacity and talent to become a global centre of TV and film production and we are committed to supporting this vital industry."