For 30 years, Prince has been trying to influence ministers

Correspondence from the Palace to Downing Street asks Prime Minister to take action over environmental matters

Attempts by the Prince of Wales to influence government policy on matters close to his heart have continued for more than 30 years, documents released by the Public Record Office revealed yesterday.

Last year, the Prince was accused of overstepping his constitutional role by bombarding ministers, including Tony Blair, with letters attacking government policy. But correspondence to Harold Wilson made public for the first time showed the Prince has been writing to successive prime ministers for more than three decades.

In a hand-written note to Wilson, dated 12 September 1969, Prince Charles called on him to do something about the plight of the Atlantic salmon, complaining that modern fishing methods were allowing them "absolutely no chance''.

Writing from Balmoral, the 20-year-old Prince said: "People are notoriously short- sighted when it comes to questions of wildlife and several species have been wiped out because no one has woken up in time to the danger. When you come up here next weekend. I shall attack you on the subject again!''

The Prime Minister later responded by assuring him that the North-East Atlantic Fisheries Commission had imposed certain restrictions off Norway. In another letter about the loss of seabirds in the north Irish Sea, Mr Wilson acknowledged that the Prince liked to be kept abreast of wildlife issues.

The young Prince's almost familiar relationship with the Prime Minister of the day was also illustrated by an earlier letter to Mr Wilson when the teenager thanked him for sending the Foreign Secretary, Michael Stewart, to speak to fellow pupils at Gordonstoun, assuring him: "There was no heckling and the questions were really quite sensible.''

The Prince's father was also no stranger to impressing his point on the Prime Minister. The body of the correspondence released by the Public Record Office yesterday is between the Duke of Edinburgh and Mr Wilson. In a string of notes, Prince Philip aired his views on everything from foreign affairs to broadcasting. The Prime Minister appeared to welcome the Prince's detailed notes, but he was not necessarily open to all his ideas.

Showing some foresight, Prince Philip urged Wilson to consider the future of pay-TV in February 1967. The Prime Minister told him he felt the collection of such revenue would be too expensive and he could not see what pay-TV would bring to viewers that was not already available on the two national channels. If it was successful, he added, it would deprive the services of some of their more popular items.

Other letters from the Duke of Edinburgh contain detailed notes on the political and economic situation of countries he had visited. He apologised for their "disjointed nature" but he suggested Mr Wilson might want to pass them on to his Foreign Secretary.

While the tenor of the letters was predominantly familiar and friendly, in one the Duke of Edinburgh wrote angrily after discovering "rather belatedly" that the Queen was to visit Malaysia but not Thailand.

Insisting that crowds of friendly people had welcomed him during his previous visit to the country, he described the decision as one that would be viewed as a "deliberate snub and a studied insult".

He added: "I realise that this has nothing to do with me but it is just that in this particular case I have some first-hand experience."