David Cameron has lashed out at the “immensely frustrating” way the European Union works, complaining that he had to “lock and load” every time he came to summits.
The Prime Minister said other countries attempted an "ambush" at the latest gathering in Brussels in an attempt to slash the British rebate by £1.5 billion.
He also demanded that the body go further to cut red tape and wasteful spending - condemning a "sexist" colouring book detailing the work of "Mr & Mrs MEP".
The Premier deployed the vivid military phrase, which refers to loading a gun, to describe his attitude to EU business as he wrapped up the two-day summit.
French negotiators are said to have argued that agricultural grants for new members should be excluded from calculations for the £3 billion annual rebate - potentially reducing it by 10%.
But Mr Cameron was adamant that the issue had already been settled in the UK's favour by EU leaders in February.
He received assurances at a meeting with European council president Herman Van Rompuy last night that the position had not changed, and final documents will make clear the rural development spending is included for rebate purposes.
Mr Cameron told a press conference: "It is, and I won't lie, it is immensely frustrating sometimes, the way this organisation works. In February, in the conclusions, it was written that the British rebate would continue as before...
"It is frankly not acceptable for it to be left to the last minute and then an attempt at reopening it, and an ambush at 1am at the end of a European Council meeting.
"I think this is no way for an organisation to conduct itself."
Mr Cameron, who has staked Britain's continuing EU membership on his ability to negotiate reform before an in-out referendum in 2017, said he would not publicly "name names" of the culprits, as they had to work together in future.
But he insisted the rebate was "completely secure".
"I am frustrated I have to go through that battle all over again. But in this town you have to be ready for an ambush at any time, and that means lock and load and have one up the spout, and be ready for it.
"And that is exactly what I did."
Mr Cameron said efforts to "restore ordinary democratic consent" in the EU were not helped by spending such as on the Mr & Mrs MEP booklet.
Some 15,000 copies have been printed for distribution at open days run by the European Parliament.
British sources said Mr Cameron had circulated a copy of the colouring book at dinner with other leaders last night to underline the level of waste.
They said German Chancellor Angela Merkel in particular had been "astounded" that taxpayers were funding such material.
Mr Cameron said today: "At first they thought that it was a hoax by the Telegraph... I had to convince them that it was a genuine, scandalous waste of money.
"It is pretty sexist at that - because Mrs MEP stops at 6pm to go shopping, Mr MEP goes on till 6.40pm."
He went on: "Without giving away too many names, a number of other European leaders were pretty appalled by this and this is the sort of thing the EU need to cut out if it is to have any chance of winning people's confidence that it spends money carefully."
The premier could not resist a dig at the European Parliament, which yesterday finally dropped its opposition to cutting the EU's 2014-2020 budget to 908 billion euro - the figure agreed by national leaders back in February.
He insisted the parliament's president Martin Schulz needed to "bear in mind" the need to restore public confidence when the legislature debated the budget deal.
Mr Cameron also argued that the EU was still not going "far enough or fast enough" to slash red tape and regulation for businesses.
He revealed he was drafting in six UK business figures on to a task force to consider how the burden from the EU could be eased.
The declared theme of the summit has been tackling the blight of youth unemployment, which has topped 50% in Greece and Spain.
European Council president Herman Van Rompuy has emphasised the need for money to be pumped into projects that could boost young people's employment chances.
But Mr Cameron has argued in the sessions that loosening labour market rules and deregulating to help firms take on more staff is crucial.