The Serious Fraud Office has requested an additional £26.5m (€33.5m, $42.4m) from the government in a bid to tackle the raft of complex investigations it has under its belt.

Britain's leading prosecutor had been expected to request extra funds this financial year, despite the fact that it had asked for £19m (€24m, $30m) earlier in 2014 to help it probe dozens of banks that are accused of manipulating key markets, such as interbank lending rates and foreign exchange.

It is able to ask for the extra funding as it only has a budget of £26.5m (€33.5m, $42.4m) – well below a selection of regional authorities' budgets – and if the cost of investigators and more lawyers is more than a specific portion of its budget.

Solicitor General Robert Buckland, a government lawyer, said: "Parliamentary approval for additional resources of £26.5 million will be sought in a supplementary estimate for the Serious Fraud Office."