A frank Foreign Office assessment of Hosni Mubarak appears in a 1980 document just released by the National Archive.
Mr Mubarak, then Egypt's vice president, is described as a "friendly and cheerful" personality but the Foreign Office warned that his "affable exterior concealed a degree of ruthlessness".
Mr Mubarak was considered by British officials to be the most likely successor to President Anwar Sadat "should anything happen to him".
It was therefore considered appropriate to make a "fuss" over his visits, which included one in September 1980 - less than a year before the assassination of Sadat by Islamic extremists opposed to peace with Israel.
Whitehall officials were cautioned not to mention Mrs Mubarak's Welsh relatives unless the matter was raised by the Mubaraks themselves, as "they may wish to play the connection down".
An evening at the ballet or the theatre was suggested as suitable entertainment "subject to the Mubaraks' tastes".
Top of the serious agenda for the visit in 1980 was a meeting with Mrs Thatcher, at which the discussion centred on slow progress towards Middle East peace, which both sides appeared to blame on Israel's settlement policy.
Secret minutes said the prime minister had told her guest that she stayed in close touch with Jewish leaders in the UK and that Israeli Prime Minister Menachem Begin's policies on the occupied territories "have no friends anywhere".
It was considered by the Jewish community, she continued, that settlement activity in the territories "was unacceptable".