Their joint declaration that the political partnership would last the distance came as one report suggested a damaging row had opened up between Downing Street and Scottish Liberal Democrats.
The latter accused the Prime Minister of "a lot of string-pulling" and "making policies on the hoof without discussing them properly first" with his Coalition partners north of the Border.
However, in another effort at showing unity, a senior LibDem source dismissed the claims as "completely overblown" and pointed out the party's outgoing Scottish special adviser in No 10, Christine Jardine, would be replaced in due course.
Last night, however, the SNP seized on the comments and linked them to the referendum battle, saying they showed the "scale of Tory domination over the strategy of the anti-independence campaign".
As the Prime Minister and his deputy announced a £9.4 billion investment in Britain's railway infrastructure, Mr Cameron used the event to emphasise how he was "even more committed to coalition government" today than he was in May 2010. "It has real purpose, a real mission," he insisted.
For his part, Mr Clegg brushed aside the row over constitutional reform, which saw a record 91-strong Tory rebellion, as one of the "bumps in the road" to be expected in the circumstances, especially on an issue which excited such strong opinions.
But he stressed: "None of that will stop us from continuing to govern in the national interest.
"We need to get on with making the big, long-term reforms and changes this country so desperately needs."
Chancellor George Osborne will later this week unveil a "programme of guarantees", using the Government's good credit rating and balance sheet, to help boost a range of additional infrastructure investments; individual projects will be announced in the autumn.
Heralding the rail investment, the Prime Minister said that in two years of partnership there had been only "one or two episodes like last week" and that the major revolt on Lords reform did not reflect deeper problems within the Coalition.
He pointed out how later in the summer the UK Government would publish a "mid-term review", which would look back over what it had done since 2010 and look forward to what it would do until 2015.
No 10 later indicated some new policies could be incorporated into the review.
Despite a weekend appeal by Mr Cameron to put aside "division and navel-gazing", senior figures still aired their views on the longevity of the Lib-Con partnership.
Graham Brady, chairman of the Conservative 1922 backbench committee, said it was "very likely" to come to an end before the next General Election, while Boris Johnson, the London Mayor, said he feared the pact was "doomed to succeed".
Asked what odds he would give on the Coalition lasting the full term, Mr Clegg said: "I would put a considerable amount of money on us seeing through until 2015 because it is what we are committed to doing."
Michael Dugher, Labour's Shadow Minister without Portfolio, said last night: "The sight of David Cameron and Nick Clegg congratulating themselves on their 'success' at a time when they've delivered a double-dip recession, shows how out of touch they are."