A former senior advisor to Prime Minister Tony Blair has added to the growing storm over the reported rift between numbers 10 and 11 Downing Street.

Mr Blair's former economics advisor Derek Scott claimed that Chancellor Gordon Brown was "obstructive and deceitful" towards the Prime Minister, hiding information about economic policy - including the content of an upcoming budget - from him.

In his book Off Whitehall, serialised by The Sunday Times, Mr Scott claimed that Mr Blair made a fatal error by ceding control over vast swathes of domestic policy to the Chancellor.

"It soon became known throughout Whitehall that, in some areas at least, the Chancellor could defy the Prime Minister with impunity," wrote Mr Scott.

The book will fuel speculation about relations between the Government's two most powerful figures after a week in which Mr Blair was thought to have angered Mr Brown by appointing his fellow-moderniser Alan Milburn as Labour's campaign supremo for the upcoming General Election.

Both 10 Downing Street and the Treasury last night brushed off Mr Scott's claims.

A Downing Street spokesman said: "We have got no intention of commenting, because it will only boost the book's publicity."

A Treasury spokesman said: "These accusations from a former No 10 aide are unworthy of serious comment."

Mr Scott's book claims:

* Mr Brown refused to divulge the contents of the 1998 Budget to the Prime Minister, saying "I haven't made my mind up". The book reports that Mr Blair was reduced to pleading "Give me a hint, Gordon".

* When Mr Blair asked for an update on his five tests on joining the euro, Mr Brown responded that it would be improper to pre-empt the Treasury's assessment.

* Treasury civil servants had to be smuggled into No 10 by the back door to avoid the Chancellor finding out about their visits.

* Mr Brown fought for weeks to block the appointment of a Treasury official, Jeremy Heywood, to Mr Blair's staff.