The bank has been closed for more than a week
Depositors in the stricken Isle of Man subsidiary of Iceland's Kaupthing Bank are petitioning three governments in a bid to rescue their savings.
Up to 10,000 people are believed to have £840m deposited in the Manx Kaupthing Singer and Friedlander (KSF).
Depositors believe the UK government's freezing of Icelandic assets led to the Manx subsidiary's collapse.
They are calling for the same 100% guarantee on their money that has been given to savers in UK subsidiaries.
The Manx Financial Supervision Commission (FSC) suspended the bank's licence on 8 October after its parent bank Kaupthing was nationalised, and its UK assets were frozen.
The Icelandic bank had issued a parental guarantee in September 2007 to take responsibility for the liabilities, including deposits, of its Manx subsidiary.
But although the UK government - which is responsible for representing the island in international matters - said British savers were protected, it has so far failed to guarantee money in offshore accounts.
Angry savers have signed a petition which states their belief that the governments of the UK, Iceland and the Isle of Man "acted irresponsibly, unfairly and in a discriminatory manner towards depositors".
They want Gordon Brown to confirm in a statement that treasury officials are "seeking the return of 100% of all deposits held within KSF (Isle of Man)".
The petition says: "The UK Government's actions in freezing Icelandic assets in the UK directly led to the failure and subsequent administration of Kaupthing Singer & Friedlander UK (KSF UK) which up to then had been a solvent and liquid entity."
Members of the Kaupthing Isle of Man Depositors Action Group were gathering in Parliament Square in London on Monday to present the petition to the UK government. Copies will also be given to Iceland and Isle of Man officials.
Although KSF (Isle of Man) was an offshore bank, many of the depositors were British citizens working overseas who found it difficult to open a UK bank account without a domestic address.
Group spokesman Stephen Thomas, 57, had £750,000 deposited in the bank after selling his house and was about to move back to the UK from Moscow, where he had been living for a number of years.
He said: "What is really annoying to thousands of savers is that Gordon Brown keeps talking of prudence, protecting savers and responsible actions by institutions.
"We are the prudent savers, we are the ones that should be applauded for being responsible with our savings, not thrown into legal limbo by an action that we should not be a part of.
"Again I wish to state, we deposited our monies in an A+ listed, solvent bank on the Isle of Man. Why are we being penalised for being responsible and prudent people?"
A court hearing on Friday will decide whether KSF (Isle of Man) is formally wound-up.