The UK Government's controversial £33 billion project for high-speed trains would see services grind to a halt in Scotland as trains are split into two.

Trains capable of travelling at up to 250mph would stop at Carstairs junction in South Lanarkshire and separate into Glasgow and Edinburgh services, according to new proposals.

The plans have been condemned by rail campaigners north of the Border who said the latest development would increase train journey times to key northern English cities and reinstate delays to cross-border services that were phased out 20 years ago.

A route map for developing the second phase of the network – extending north from Birmingham to Leeds and Manchester by 2033 – includes cutting journey times from Glasgow and Edinburgh to London to 3hrs 38min. This is up to half-an-hour quicker than current fastest services.

Plans to build a 250mph railway, known as HS2, between London and Birmingham by 2026, have already been published and proposals for a second Y-shaped network have now been put out to consultation. The final route is due to be chosen by the end of 2014.

But they have been criticised by business leaders and politicians who said they offered few benefits north of the Border and called for a high-speed network to be extended to Scotland.

Liz Cameron, chief executive of Scottish Chambers of Commerce, said: "Whilst marginal benefits will accrue to Scotland in terms of slightly shorter journey times if the Y network is completed on schedule in 2033, the fact remains that figures from the Department for Transport (DfT) show central Edinburgh to central London journeys will still be quicker by air than by rail two decades from now.

"Against a background of pressure on Scottish air links to London, from capacity issues at Heathrow, and the fact that HS2 will deliver significant connectivity benefits for English cities, this could lead to Scotland becoming even more marginalised."

Gordon Matheson, leader of Glasgow City Council, said both Glasgow and Edinburgh would be put at a "huge economic disadvantage" under the current proposals.

The SNP and Scottish Labour both condemned the HS2 announcement as unambitious, saying it was essential that plans to include Scotland in the network were progressed more quickly.

The Scottish Government has also attacked plans to terminate trains from London at the Scottish capital, cutting off through services currently provided by East Coast to Dundee, Aberdeen and Glasgow. Similar proposals were dumped last year after they provoked uproar.

Ministers agreed a year ago to develop a timetable by 2015 for bringing a high-speed rail network north of the Border. It could cut London to Scotland journeys to 2hrs 30min.

However there is scant detail on how this might be achieved. Keith Brown, Scotland's Transport Minister, said he was still pressing the HS2 company to take forward its high-speed rail plans, to include a "phase three" option to Scotland in its remit.

A Transport Scotland spokesman later denied claims by the DfT that its

proposals were in line with the wishes of the Scottish Government agency.

He said: "Transport Scotland has made no statement in preference of Scotland being served by high-speed rail using a West Coast Main Line alignment. Nor have we supported using a splitting/joining service to serve both Edinburgh and Glasgow as it would add a journey time penalty to Scots services.

"The Government is also clear on the need to preserve through services between London and destinations north of Edinburgh."

A spokesman for HS2 said: "Scotland will benefit from high-speed services as soon as Phase One of the route between London and the West Midlands opens in 2026, as there will be seamless transition of trains on to the West Coast Main Line.

"Once Phase Two is completed, we expect journey times to and from London will be reduced by at least 30 minutes without the need to change trains.

"These better services would help provide benefits to the Scottish economy of around £3bn."

He added the DfT is planning to take forward a study in collaboration with Transport Scotland which would "consider Scotland's aspirations for high-speed rail."