Tony Blair leapt to the defence of the Prince of Wales today over accusations that the "dissident" heir to the throne was too ready to meddle in politics.

But Mr Blair, criticised in one of the Prince's journals for his Government's obsession with market research, could not resist a little dig.

Asked at his regular Downing Street press conference if the Prince had overstepped the bounds of his role, he replied: "I don’t know if I can answer that question until I’ve had the focus group."

The Prince has come under fire from Labour MPs after his former press chief revealed in the High Court that Charles saw his job not just to raise funds and carry out royal duties, but to express his views on contentious issues like a dissident challenging the prevailing consensus.

Clarence House is pursuing a claim against The Mail on Sunday, which published excerpts from a journal on the Hong Kong handover, for breach of copyright and confidentiality and demanding the return of seven other unpublished diaries. The first stage of the case, in which the Prince's team has argued for a summary ruling, ended today with the judge reserving his decision.

Asked about the row, the Prime Minister said: "I think that Prince Charles does an amazing job for the country. If you look at the Prince’s Trust, it’s probably one of the most successful voluntary sector organisations in the world, never mind in this country, and I think he’s perfectly entitled to express his views and personally I find no problem with it at all."

The 1997 journal on the handover of Hong Kong - entitled The Great Chinese Takeaway - was released yesterday at the High Court, where reporters were given an hour to take notes and copy excerpts.

In it the Prince complained about being made to sit in club class on the jumbo jet to Asia while political dignitaries sat in first class on the floor below. He also lamented the decision to "ex-commission" the Royal Yacht Britannia, which made its final overseas trip for the handover ceremony.

Most controversially, he expressed fear for Hong Kong's future under Chinese rule, dismissed the Chinese leadership as "appalling old waxworks" and described how "goose-stepping" Chinese soldiers hauled down the Union Jack.

Mr Blair said: "It is, I think, completely unreasonable not to expect that he has views or that he transmits them to government ministers, but they are not views that I have ever, ever regarded as party political.

"For example, he will raise issues sometimes to do with the rural community or issues to do with voluntary organisations in the UK, which I actually find perfectly helpful. I think you can get a very exaggerated view of how much this happens. I personally don’t think it has ever caused any difficulties for ministers. I have never found it difficult at all, I have to say."

The Prince's team has been arguing in the High Court that the journal - and seven other unpublished diaries that it wants The Mail on Sunday to return - are private documents that were circulated to a select circle of friends and acquaintances. The newspaper's lawyers have argued that documents are of public interest and cannot be merely dismissed as extended holiday ramblings.

Mr Justice Blackburne reserved his ruling at the High Court after hearing that the Prince writes journals on foreign trips to send to his friends and family like other people write letters and postcards. Hugh Tomlinson, QC, said that his client was entitled to keep those private thoughts and observations secret and arguments that the journals should be published in the public interest were "far fetched".

Mr Tomlinson has been asking for a summary ruling, legal device whereby a finding can be made without a trial if it can be shown that the defence has no chance of success.

Lawyers in the field say the facts are clear cut and the Prince should succeed in his broader claim, but they say that because of the high profile of the claimant and the issues of pess freedom, the judge may call for a full trial - which would leave the Prince open to cross-examination in the witness box should he decide to give evidence.

This eventuality was mentioned in the final moments of the hearing today as Mr Tomlinson referred to the disagreement between the two sides over the number of people were sent the journal.

The judge, commenting on what would happen if the issues had to be contested, said: "The other side is rather hoping the Prince of Wales would be turning up and be cross-examined." Mark Warby, QC, representing The Mail on Sunday, rose to his feet with a smile and said: "That is entirely a matter for him."

There was one piece of good news for the Prince today. When the subject of the Hong Kong journal was raised at a regular Foreign Ministry press briefing in Beijing, spokesman Liu Jinchao said: "I have not read the private diary. We are not interested in the diary you talk about."

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