By Nick Assinder BBC News Online political correspondent

Thanks to some anonymously sourced tapes of Peter Foster's telephone calls, the full extent of the convicted conman's attempts to squeeze the prime minister's wife have been made public.

Who was bugging his calls and who then passed them onto the Sun newspaper is a matter of huge interest.

Downing Street�s latest tack has been to try and turn this hugely-damaging row into a straightforward battle between good and evil

But it is a question that will almost certainly never be answered.

Under usual circumstances the old saying: "who stands to gain?" might point in the right direction.

But it is not so simple in this case.

One reading suggests that the Blair camp - that must now include Mrs Blair, the prime minister, Downing Street and even the government - gains an advantage.

Downing Street's latest tack has been to try and turn this hugely-damaging row into a straightforward battle between good and evil. Cherie and the conman if you like.

For two days now, the line out of Number 10 has been that Peter Foster is a convicted fraudster and has been setting the agenda all along.

Vendetta

The subtext is that nothing emanating from his camp can be believed.

The argument goes that he has been trying to use his friendship with Cherie Blair's friend and "lifestyle guru" to his own advantage.

Whatever the truth of the matter, however, the battleground has shifted once again

Now he has failed, he is using the media to pursue a vendetta against Mrs Blair with the aim of taking her down with him.

And his telephone conversations with his mother certainly seem to support that view.

An alternative reading, however, suggests the tapes prove what many have suspected all along - that Cherie Blair did use him as a financial adviser and tried to help him out in his deportation case.

Shift

She must have known of his past long before the newspapers got hold of the story and has been covering up for it all ever since.

Foster documents not read

The phone conversations can also be used to support that theory.

Whatever the truth of the matter, however, the battleground has shifted once again.

While Tony Blair challenges his accusers to take their allegations to the police - a quite extraordinary situation for any prime minister to find himself in - Downing Street is turning the story into a straightforward battle between Cherie and Peter Foster.

Presumably the hope is that, in the escalating claims and counter claims, the allegations surrounding Cherie�s conduct in relation to her blind trust and the deportation case itself will get lost.

Questions

It is a tempting route to follow. Stories about goodies versus baddies are always easier to follow and to promote.

But there are still very serious allegations at the centre of this row and the fact that the detail is arcane and boring will not stop people asking questions.

After all, anyone who remembers or was close to the Westland row in 1985 will recall how mind bendingly complex and dull the arguments over this little west country helicopter company were.

Yet one senior Tory minister, Michael Heseltine, sensationally stormed out of cabinet over it and it came within an ace of doing for the then prime minister - none other than the Iron Lady, Margaret Thatcher, herself.

Why? Because it suggested lying, impropriety and cover up in Number 10.