TREASURY chiefs routinely accepted “cosy” dinner dates with lobbyists for banks even as they were being investigated for financial misconduct, an explosive new report reveals today.

An investigation by the National Audit Office also shows arms manufacturers are among the most frequent providers of hospitality and gifts to government officials.

The Whitehall watchdog found that senior civil servants accepted 3,413 corporate freebies between April 2012 and March 2015.

Mandarins were most likely to be treated to dinner and drinks, with a whopping 2,656 meals registered — including at luxury 5-star venues such as the Quirinale, Savoy Grill and the Athenaeum.

They also registered luxury gifts such as iPads, sports tickets and bottles of champagne.

A Fortnum and Mason hamper, a painting worth £300 and a tour of the Warner Bros Harry Potter Studio were among more extravagant items exposed.

In one case an official was made to surrender a £300 Mont Blanc pen to the Department for Business, Innovation and Skills.

NAO chief Amyas Morse said that while it is “reasonable” to accept gifts and hospitality, they could “present a risk of actual or perceived conflicts of interest.”

The report highlights serious cases which the NAO warned “might be considered to be a conflict under the Civil Service guidance.”

It reveals that “the Bankers’ Association (BBA) was among the most frequent providers of hospitality, at the same time that some of its members were being investigated in the UK for market manipulations and by the competition regulator.”

The association provided gifts and hospitality on 21 occasions, including lunch dates with the permanent secretary to the Treasury Sir Nicholas Macpherson and his deputy John Kingsman.

Officials have also accepted freebies from Barclays and HSBC — both members of the BBA which have been fined by the Financial Conduct Authority — on 49 occasions since 2012.

Details of the close relationship between senior government officials and the banking lobby come just a week after it emerged Tory ministers had met Google bosses 24 times in the last two years.

A Cabinet Office spokesman said the report is proof that “this government is the most transparent ever and publishes an unprecedented range of information about gifts and hospitality.”

But Labour MP Dawn Butler said: “The Tories should be standing up for consumers and tackling bad practice, but this looks like a relationship that’s just a bit too cosy.

“Once again this government proves it is not on the side of working people.”

The report also examined gifts and hospitality received by bosses at the Defence, Equipment and Support, which is described as a “bespoke trading entity within the Ministry of Defence (MoD).”

The MoD department accepted £100,000 worth of freebies from 600 organisations last year.

But the most frequent supplier is arms manufacturer BAE Systems, which lavished officials on 581 occasions.

The NAO said that also raised a possible conflict of interest as the company is a “major supplier to government.”

They also raised concerns over the “proportionality” of allowing arms manufacturer Lockheed Martin to pay for wine at the Skills Funding Agency Christmas lunch for two separate years.

Campaign Against Arms Trade spokesman Andrew Smith told the Star: “This is another example of the politically intimate and compromising relationship between arms companies and Whitehall.

“These companies wouldn’t be buying these gifts and spending this money unless they expected something in return.

“BAE isn’t just a major provider to the government, it is also profiting from the destruction of Yemen and working with ministers and civil servants to push for even more arms to human rights abusing regimes like Saudi Arabia.”