By Nick Assinder BBC News Online political correspondent

It just gets worse. It has emerged that Cherie Blair took a personal interest in the deportation case against convicted conman Peter Foster.

This is the man who acted for the prime minister's wife in her purchase of two flats in Bristol but who, she insisted, she hardly knew.

And, she particularly insists, she most certainly did not know about his checkered past when she used him to buy the flats.

This affair is now striking at the heart of the government

Had she known this, she may have been more circumspect in her dealings with him, she has stated.

But it has been revealed that she made a call to his solicitor to ask about the deportation proceedings before he got involved in the flat purchase.

The innocent explanation to this latest bombshell is that Mrs Blair simply wanted to reassure her friend Carole Caplin that her boyfriend's case was being treated properly.

'Stretching credulity'

Why she thought that may not be the case is an open question.

The less than innocent interpretation is that she was getting personally involved in the proceedings - clearly a pretty significant "favour" for someone she didn't know.

Either way, the idea she could have made the call without knowing the details of Mr Foster's past seems to be stretching credulity to breaking point.

So, once again in this twisted affair, it is the issues of honesty and judgement that have raised their heads.

First Mrs Blair insisted, through Downing Street spokesmen, that she had never used Mr Foster as a financial adviser.

The block of flats in question

When it emerged she had, and that the spokesmen had been "misled" by her, she claimed she knew nothing of his past and had only dealt with him for a couple of weeks.

Now it appears she had had dealings with him for far longer than two weeks and that she must have known something about his background when making the call about his deportation.

'Awkward questions'

Meanwhile, a separate question has been asked over her use of cash in a blind trust to buy the flats, one of which was purely for investment purposes.

This has dragged her husband into the affair because it is being claimed it was a breach of the ministerial code of conduct.

This affair is now striking at the heart of the government.

Pressure for Blair statement

The prime minister has become involved for the first time and normal business is being overshadowed by the revelations.

The question on everybody's lips in Westminster is why, once the first details of the "misunderstanding" had emerged, Mrs Blair didn't simply put her hands up and tell the whole truth.

After all, there is still no suggestion she has done anything illegal or improper.

Instead, it appears she has tried to avoid answering awkward questions and even succeeded in making Downing Street civil servants appear liars.

'Dismay'

And there is no sign that this affair is at an end.

Each time Downing Street has attempted to draw a line under it there has been yet another revelation to re-open it, and even escalate it.

It is being claimed that neither the prime minister's right hand man and spinner -in-chief, Alastair Campbell, or his wife Fiona Millar, who works as Mrs Blair's aide, have fallen out with Mrs Blair over her relationship with either Carole Caplin or Mr Foster.

But there is no doubt that many in Downing Street have long been dismayed over Mrs Blair's relationship with the former topless model and fitness advisor - even seeing it as an accident waiting to happen.

Well, that accident has now happened and Mrs Blair's handling of it has ensured it has turned into a multiple pile-up.

There can be no certainty that there will be no more revelations in coming days, and the refusal of both the prime minister and his wife to make personal statements on the affair are looking increasingly untenable.

This now looks like an embarrassment running dangerously out of control and threatening to turn into a genuine crisis.