Coalition MPs have turned to Twitter to express their frustration at Labour for using delaying tactics to keep the House of Commons sitting into the small hours.
Liberal Democrat Norman Lamb, a parliamentary aide to Nick Clegg, admitted falling asleep while doing casework as a marathon debate on the Finance Bill stretched on until 4am.
Many Tory MPs took advantage of the long session to attack the alternative vote Yes campaign, which has claimed a change in the voting system would make MPs work harder.
Because debate on the Finance Bill, which enacts the Budget, cannot be cut short under Commons rules, Labour were able to keep the debate going.
Mr Lamb wrote on Twitter: "Fell asleep signing casework letters in-between votes!"
Tory Harlow MP Robert Halfon said he was "keeping awake courtesy of Diet Cokes". His fellow Conservatives Nick de Bois and Louise Bagshawe mocked the pro-AV camp's claims about electoral reform and "lazy" MPs.
Enfield North MP Mr de Bois wrote: "So here we are in the Chamber at 3.30am... and apparently under AV MPs will work harder." Corby MP Ms Bagshawe, using the "hashtag" symbol adopted by the Yes campaign, wrote: "So, #yestoAv will make lazy MPs work harder! #stillworkingat3:30am."
Lib Dem St Austell and Newquay MP Stephen Gilbert expressed his frustration at a small number of Labour MPs who were prolonging the debate, claiming "11 opposition MPs currently sat on benches opposite delaying whole House - deliberate tactics from a so-called 'modernised' Labour Party".
Tory West Worcestershire MP Harriet Baldwin wrote: "When Labour do these filibusters, it is the HofC (House of Commons) staff I feel bad for." With local elections and the AV referendum on Thursday, Ms Baldwin claimed the motivation for Labour's actions was "so that we are too tired for election day".
Labour frontbencher Kerry McCarthy noted that "lots of ministers kept here to vote by Tory whips. They won't be happy".