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".
Mr Cameron 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 on Thursday 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."