LORD Owen, the former UK foreign secretary, has spoken of his opposition to nuclear weapons stationed on the Clyde.

The former leader and co-founder of the Social Democratic Party described Trident as an "expensive financial inroad into our conventional defence effort".

He discussed replacing Trident while delivering the inaugural Hennessy Lecture, established in honour of the constitutional historian and cross-bench peer Peter Hennessy.

The former navy minister, who was for 26 years the MP for the naval city of Plymouth, believes that replacing Trident is a too costly and that cruise missiles conventionally armed but capable of carrying nuclear weapons, if needed at times of global tension, was "a prudent insurance policy".

And he indicated that many senior serving officers believe that any Trident successor will have a crippling effect on spending for conventional defence planning.

"The Scottish Nationalists support NATO despite their opposition to Trident successor submarines being built and for nuclear weapons to come in or out of the Clyde. A British minimum deterrent can in fact be retained without nuclear weapons being on the Clyde," he said.

While he was in office he privately advocated a system based on cruise missiles for a fraction of the cost of Trident.

New Astute class submarines which began to go into Royal Navy service five years ago are already fitted with cruise missiles. In times of emergency, he has said, their conventional warheads could be switched for nuclear ones.

"I see NATO as essential and Trident as an expensive financial inroad into our conventional defence effort. Supersonic cruise missiles conventionally armed, which may well be designed fairly soon, but capable of carrying nuclear weapons at times of global tension, I see as a prudent insurance policy," he said.

Lord Owen said he hoped Labour MPs would have a free vote over the "costly" 'main gate' decision to replace Trident to be taken in Parliament.

"We will see many MPs, in my judgement, correctly voting against, whether Labour, SNP, Liberal Democrats, Plaid Cymru or Green.

"It would not surprise me if a few Conservative MPs and others abstained because they know that there are many senior serving officers and military commentators who believe the Trident successor, on top of two large aircraft carriers being built, will cripple other parts of a balanced British conventional defence strategy."