Jeremy Corbyn and David Cameron
Labour leader Jeremy Corbyn quizzed the prime minister over HMRC staffing levels Reuters

David Cameron faced sustained attacks from Labour and the SNP over the staffing levels of the UK's tax watchdog during Prime Minister's Questions (PMQs), as the fallout from the explosive Panama Papers leak continues.

Jeremy Corbyn continually pressed the Conservative leader on the issue after Cameron admitted to selling shares in his late father's offshore investment fund, Blairmore Holdings.

The prime minister insisted that the government has given £800m ( $1.14bn) more to HMRC in a bid to crack down on tax evasion and avoidance. But the Labour leader pointed out that the 2016 budget showed the department's funding will fall from £3.3bn to £2.9bn by the end of the parliament in 2019/20.

"It's not how much money you spend on an organisation, it is how many people you can have out there collecting people's taxes and making sure the forms are properly filled in," Cameron replied.

He added: "He asks about what we are doing on the Panama Papers, we have a £10m cross-agency review to get to the bottom of all the relevant information... in terms of taking action in tackling tax havens, this government has done more than any previous one."

Panama Papers: The 11.5 million-page document leak explainedIBTimes UK

The SNP's leader in the House of Commons, Angus Robertson, also pushed Cameron on the matter. The nationalist claimed around 3,250 Department for Work and Pensions (DWP) staff are investigating benefit abuse, while just 300 HMRC workers are probing tax evasion and avoidance.

However, Cameron dismissed the figures as "completely bogus". The prime minister also insisted that the UK's new register of beneficial ownership would be open to the public and stressed Britain's crown dependencies and overseas territories (apart from Guernsey and Anguilla) would let HMRC officials look at their registers.

But Corbyn pointed out the government of the Cayman Islands has declared victory over the beneficial ownership agreement.

"This is what we wanted, this is what we have been pushing for three years for, a disaggregated system which leaves the beneficial ownership information intact with the service providers but accessible by the general registry and accessible by the law enforcement agents in Cayman," premier Alden McLaughlin reportedly said.