MSPs will be told this week the cost of the new Scottish Parliament is about to soar yet again, probably taking it to more than (pounds) 400m.

The news will be met with widespread dismay and renewed argument about the whole project, which is now going to cost at least 10 times the original estimate by Donald Dewar of (pounds) 40m.

The cause of the latest increase is a technical problem in the lightwell area of the debating chamber and public entrance involving specialised glazing. Restricted access has led to a backlog of work and expensive delays involving a queue of contractors.

Fears of another huge increase in the final price from the most recent estimate of (pounds) 375m were confirmed to The Herald last night and are certain to cause another explosion of public anger.

A formal estimate of the latest price is expected any day now from the Holyrood project's quantity surveyor. A source told The Herald: ''It does not take the brain of Britain to see the cost going up again and this time it will probably break the (pounds) 400m mark. We still don't know an exact figure. How long is a piece of string?''

The latest delays mean the Holyrood building designed by the late Enric Miralles is now set to be completed three years after the first scheduled date for completion.

The lightwell area is an expanded open basement section of the project described as being contained in a ''tight nest'' of structures ranging from three to seven storeys, including debating chambers and towers.

George Reid, the presiding officer, is to write to MSPs on the parliament's finance committee confirming a further delay, although it is thought his letter will not contain a new figure for the final estimated cost.

He will confirm that the parliament's Holyrood progress group, which oversees construction, has been briefed that this especially complicated part of the project means it is ''logistically very difficult to access/ egress'' materials and plant. Safe working practice means work is limited to one action at a time, leading to delays and more expense.

The news follows a statement last week from John Home Robertson, a Labour member of the progress group, that Bovis Lend Lease, the construction managers, were reporting ''significant problems'' around the north lightwell and public stair.

This came after Bovis had predicted the whole project would be ready for the parliament to move in during the Easter recess next year.

Mr Home Robertson said then that delays could jeopardise the timetable and he admitted that ''related programme information'' was still emerging, raising fears of even more delays and expense.

''We expect the construction and design team to do everything in their power to fulfil their earlier assurance to complete the project within an acceptable timescale, and we will be having further meetings with them next week,'' he said.

Mr Reid returned from holiday on Monday and convened a series of meetings of those concerned with the project. It is thought his letter about the latest delays will go to Des McNulty, finance chairman, tomorrow.

In April, Jack McConnell publicly conceded that the cost of the parliament building would rise to around (pounds) 400m. However, five days later he corrected himself and claimed he had no reason to believe that the cost would be any more than the (pounds) 338m already quoted at the time.