LORD Owen, the former foreign secretary believes a minimum defence deterrent can be retained on the Clyde without nuclear weapons.

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

The Herald: The fleet of four Vanguard-class submarines which carry the Trident missiles is due to be replaced from 2028

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

And he indicated that many senior serving officers believe the Trident successor will have a marked impact on 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."

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.

The Herald:

"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 he hoped Labour MPs would have a free vote over the "costly" main gate decision over whether to replace Trident to be taken in Parliament because he said it "was so obvious there are differences of opinion".

"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."