UK-resident clients of Swiss banks who have yet to declare assets to HM Revenue & Customs, the UK tax authority, should take urgent action, according to Equity International Asset Management, the Geneva-based wealth advisor.

Under new UK-Swiss legislation, commonly referred to as “Rubik”, UK residents must either declare all assets to HMRC or pay a significant level of withholding tax to retain anonymity. Amounts subject to future withholding tax and the one-off levy for historical UK non-compliance must be finalised by 31 May 2013.

Failure to comply could lead to penalties of up to 200 per cent of the tax outstanding and, in extreme cases, up to seven years in jail. “While Swiss banks are writing to clients, the onus is on individuals to contact the banks and get the process moving,” Jacques Leuba, director of wealth structuring and estate planning, said in a statement. Equity International has published a free guide entitled Solving the Puzzle: The Impact of the Rubik Legislation on UK Resident Clients of Swiss Banks.