KARACHI, Pakistan, July 5— The Government of Pakistan disclosed today that it had lodged a protest with Britain charging that a concerted anti Pakistan campaign was under way in London.

The Pakistani radio said the protest was delivered Saturday to the British High Commission, or embassy, in Islamabad.

Statements by Britons and groups of Bengali separatist sympathizers living in London are directed toward fragmenting Pakistan, the note said.

Pakistan particularly complained of a speech delivered June 21 by the British Foreign Secretary, Sir Alec Douglas Home, who said aid to Pakistan should be withheld pending a political settlement for East Pakistan.