Last year Scotland lost three men whose contribution to the current shape of the country's theatre most of the populace is probably less than fully aware of.

The man who invented A Play, A Pie And A Pint, David MacLennan, is probably the best known name, but the work of Ian Smith, whose Mischief La Bas company animated the city of Glasgow and beyond with petrified Christmas Trees and the lab-coated Elvis Cleaning Corps, was probably seen by even more people.

And Adrian Howells, whose audience for his intimate performances was often explicitly limited to a single person, may have had more influence on the shape of the work of Scotland's current crop of young theatre-makers than either. They all left us much too soon, but in the first months of 2015 their legacy could not be more apparent.

This past week at the Arches in Glasgow has seen this year's Into the New presentation of work by students from the Contemporary Performance Practice course at the Royal Conservatoire of Scotland. Howells, who began his career in Scotland as an assistant to Philip Prowse at Glasgow Citizens, was one of the great mentor figures to this strand of bold, personal, devised theatre-making that has been one of the most distinctive products of the Conservatoire in recent years, and informs the work of our successful children's theatre companies as much as it does more "adult" live art performances.

He was also a research fellow at Glasgow University, and the young people who are coming out of the Theatre Studies department there full of creative ambition are light years away from the bookish students of "Drama" I studied with (and was) in my years there. Howell's loss was very keenly felt by staff and students there too, but the work many of them are producing continues his influence in the most subliminally celebratory way. I also expect to detect it in the work of Tramway's Herald Angel-winning youth company, Junction 25, when their new show is revealed in March.

Ian Smith's children, Stanley and Lily, are alumni of Junction 25, but that is not the only way you would recognise his DNA in the company's work. A master of the oblique strategy to engage an audience, Smith was also a great demystifier of the art of performance. That twin-track approach can be seen in the performances of Rob Drummond, Gary McNair, Nic Green, and Tashi Gore and Jess Thorpe of Glas(s) Performance (leaders of the Junction 25 troupe) and many more for whom the Arches and Tramway are laboratory spaces.

Oran Mor in the West End serves a related, if less experimental, function, with A Play, A Pie And A Pint, MacLennan's concept to introduce London pub theatre to Glasgow, which has grown arms and legs all over the nation and even overseas in a way that he could not possibly have envisaged.

Of course that is only the most recent part of his legacy, because his founding membership of 7:84 Theatre Company (Scotland) and then co-creator of Wildcat Stage Productions gives him a share of responsibility for a style of theatrical production that, although derived from the work of Joan Littlewood, came to be seen as particular to theatre in Scotland. If it was perhaps thought a little dated at the start of the new century, it has unarguably been thrust centre stage again thanks to the phenomenal success of the National Theatre of Scotland, and the work for that company of directors John Tiffany, Graham McLaren, Wils Wilson and - with Rona Munro's James Plays - now the company's new artistic director Laurie Sansom.

We'll surely be seeing much more of that distinctive Scottish brand of theatre from the NTS in the future, as it has been such a patently exportable success story, but more immediately we'll see the new season of A Play, A Pie And A Pint when the first new piece for 2015, Butterfly by Anne Hogg, opens on Monday January 26. The first half of 2015 includes work by some top names including Paddy Cuneen, Rob Drummond, Davey Anderson and Peter Arnott, and ends in June with Morag Fullerton's follow up to the international hit that was her pocket-sized Casablanca, a "Lunchtime Cut" of Sunset Boulevard.

This is the first season overseen by MacLennan's protege and successor Susannah Armitage, and it seems beyond any doubt that the concept is in safe hands and that the loyal PPP audience will stay true.

One thing is quite clear: all three men of the theatre that we lost last year have left a legacy in the theatrical output of Scotland for years to come, a legacy that is more evident than most of what is often labelled with that recently much-overused word.