I'm focussed on economy, insists PM

In an apparent allusion to the row over the resignation of his special adviser Damian McBride, the Prime Minister admitted some of the problems he had to deal with were "annoying".

Mr Brown spoke out as Chancellor Alistair Darling puts the final touches to Wednesday's crucial Budget.

And as MPs headed back to Westminster following a difficult Easter break for the Government, Mr Brown said he would not be distracted from the economy by "all the other diversions in politics and all the problems that happen - and some of them are difficult and some of them are very worrying and annoying".

Mr Brown was joined at Loughborough University for the launch of the Government's strategic economic and industrial investment plan by Business Secretary Lord Mandelson. He said the Government would concentrate on the big issues "and not allowing itself to be distracted by every media squall" sent its way.

Mr McBride, who was one of Mr Brown's closest aides, was forced to quit following the disclosure of emails he sent suggesting an internet smear campaign against leading Conservatives.

Meanwhile, Conservative leader David Cameron said he was "really bl**dy angry" about the allegations in the McBride emails and repeated Tory calls for Cabinet Secretary Sir Gus O'Donnell to carry out an inquiry into the affair.

Mr Cameron said: "I was incredibly angry about it and I said that at the time. It wasn't some sort of tactic, me wanting the Prime Minister to say sorry. I felt really bl**dy angry about it and I wanted him to acknowledge that and he did.

"I think the fact that he has said sorry is important, but what he has to do is work out what is going on in 10 Downing Street, because what we seem to be being told is that it is some sort of lone gunman operating alone.

"There has been no inquiry, no investigation, no one seems to be looking at his email inbox and actually getting to the bottom of who knew what, who was involved in this."