Nick Clegg and David Cameron's efforts to reunite after a fortnight of infighting suffered a setback when it emerged that the loss of 2,400 jobcentre posts is to be announced today, just a day after they jointly announced a £60m youth unemployment initiative.

The Guardian has learned that the job cuts at Jobcentre Plus over the next 12 months include the loss of 17 benefit processing centres and five contact centres, representing nearly 20% of staff.

The losses are part of a drive to rationalise properties in the jobcentre estate. Officials said that no one would be made forcibly redundant and that no high street jobcentres would be closed.

The Department for Work and Pensions said: "We will not comment on leaks. When making any announcement to staff we do so in the proper way."

The revelation comes the day after Clegg and Cameron came together for the first time since the battle over the AV referendum to announce a package of measures to fight youth unemployment.

Meeting at the Olympic Park in east London, the prime minister and his deputy announced a £60m programme to boost work placements for 16- to 18-year-olds.

A subdued-looking Clegg said the government could not "wave a magic wand" to create jobs, but it could "intervene at critical points". He announced a pilot, involving 50,000 youngsters over two years, of six-week intensive periods of support – including help with training, childcare and presentation skills – with a guaranteed job interview at the end.

Liam Byrne, the shadow work and pensions secretary, denounced the job losses. "Days after the Bank of England warned the economy is slowing down, the government is cutting the very people helping get Britain back to work."

He added: "Nick Clegg tried to relaunch his credibility with a promise to get young people back to work. Why didn't he tell us his scheme was paid for by sacking jobcentre staff?"

Clegg and Cameron worked hard to give the impression of a government back on track and functioning as normal, despite suggestions of a more businesslike atmosphere between the coalition partners.

After the Lords defeated directly elected police commissioners on Wednesday night, Clegg said he would overturn the Liberal Democrat-inspired decision. The government was defeated largely due to a small group of Liberal Democrat peers voting with Labour. Clegg vowed to overturn the defeat in the Commons, telling his party it had a "duty" to implement policies – even if Tory-led – that were in the joint programme.

One frontbench Lib Dem peer, Lord Bradshaw, said he might resign as transport spokesman rather than back down.

Giving evidence to the Commons political and constitutional reform committee, Clegg said his commitment to reform was undimmed despite defeat in the AV referendum.

He stressed that his imminent proposals on an elected House of Lords will be designed to create an all-party concensus, adding he did not intend to change the powers of the Lords in relation to the Commons. Clegg said: "I am very clear we should not seek to change the functions and role of the House of Lords. It should remain a body of scrutiny and review."

He also said he favoured an update of the coalition agreement in the mid-point of the parliament, and would like to see a focus on better work-life balance, as well as a greener government.

Some Liberal Democrats fear another coalition agreement will do little to help the party rebuild its identity. Others argue it would be a chance to demonstrate Lib Dem influence on policy.

With some polls now showing his party's support dipping below 10%, Clegg said: "Polls go up and down. People's popularity goes up and down, parties' popularity goes up and down.

"At the end of the day, how will we be judged? We will be judged about whether we have sorted out the mess we have inherited and restored a sense of optimism, of prosperity, of jobs for this country. It is a job we have started and we are going to see it through."

Privately, Liberal Democrats remain shocked at the extent to which they have taken a hit in the polls while Cameron has remained unscathed. The prime minister insisted voters should judge the success of the Tory-Lib Dem partnership on what it had delivered after five years, and not day-to-day "fripperies".