Mr Clegg faced a split within his party over the referendum vote
Three Liberal Democrats have resigned from their frontbench roles after they joined another 12 MPs in defying party orders over the EU referendum vote.
Leader Nick Clegg had ordered his 63 MPs to abstain in the vote on calls for a referendum on the EU Lisbon Treaty.
But frontbenchers Alistair Carmichael, Tim Farron and David Heath all stepped down so they could vote in favour. Mr Clegg immediately revamped his team.
The Conservative call for a referendum was defeated by 311 votes to 248.
Mr Clegg wants a wider referendum on whether Britain should remain in the European Union.
He told his MPs to abstain from Wednesday night's vote on whether to hold a referendum on the EU Treaty.
'Respect their views'
Thirteen Lib Dem MPs defied the party's whip to side with the Tories. In a later, separate vote on a referendum, proposed by Labour's Ian Davidson, 14 Lib Dems rebelled.
Altogether, 15 MPs ignored Mr Clegg's calls for abstentions.
The resignations are seen as a test of his authority, less than three months after he became leader.
Mr Clegg said he "greatly regretted" the loss of the three spokesmen, adding: "Though we have disagreed on this issue I fully understand and respect their strongly held views on the subject."
"However, as they have recognised, the shadow cabinet cannot operate effectively unless the principle of collective responsibility is maintained.
"I am grateful for their offer of strong support from the backbenches, and I know that they will all play a very significant role in the future of our party."
Within minutes of the result the party released exchanges of letters between the three and Mr Clegg.
He also said that countryside matters, previously looked after by Mr Farron, would transfer to environment spokesman Steve Webb.
Justice matters, previously looked after by Mr Heath, will be transferred to form part of home affairs spokesman Chris Huhne's responsibilities.
Mr Heath said: "I couldn't support a position taken by the party on a three-line whip and therefore consequences are inevitable and I am now on the backbenches as a result.
"I've been personally committed to a referendum for a very long time and its not just what was in the last manifesto, its what I personally feel. And I wanted to be honest to myself and my constituents."
Mr Carmichael's role as Scotland and Northern Ireland spokesman will be looked after by international development spokesman Michael Moore.
Eight of the other rebels are junior party spokesmen.
They are : John Pugh (Treasury), Annette Brooke (children, schools and families), Richard Younger-Ross (culture, media and sport), Martin Horwood (environment), Greg Mulholland (health), Sandra Gidley (health), John Leech (transport) and Mark Williams (Wales).
The other four, who have not got posts, are John Hemming, Paul Holmes, Andrew George, and Mike Hancock.