ISLAMIC State terrorism poses an “existential threat” to Britain’s way of life and western civilisation, so must be degraded by UK airstrikes in Syria, Ruth Davidson has argued ahead of tomorrow’s key Commons debate.

The Scottish Conservative leader, in London to meet Tory colleagues and attend, for the first time, the 1992 backbench committee, said the UK was already in a war with IS and this was now a time for “moral courage and genuine leadership”, which David Cameron was showing.

Asked, given that in recent years the UK’s involvement in Iraq and Libya had not produced the desired outcomes, why she was in favour of extending airstrikes to Syria, Ms Davidson said: “I don’t think it was widely reported but I was against the Iraq intervention. I marched against the Iraq intervention; it is the only march I’ve ever been on…”

She went on: “People have related Syria to the threat level, whether it would increase or decrease the threat to the UK, for me that’s not the question. The question is we accept IS is a threat to the UK, do the airstrikes increase or decrease their capacity to carry out the threat that they have?”

Ms Davidson said airstrikes would “diminish their capacity to strike against a country, whose way of life they said they want to destroy”.

She stressed: “This isn’t a war that we’ve chosen; this is a war that we’re in. Paris didn’t choose what happened to it. It could have been Edinburgh, it could have been Birmingham, it could have been Cork or Dublin, Ghent or Bruges, Munich or anywhere else.”

The party leader described the decision by the German government to engage in military action as “extraordinary”.

Angela Merkel’s cabinet has decided to back plans for military support in the fight against IS terrorists in Syria.

Tornado reconnaissance aircraft, a naval frigate and a 1200-strong force will be sent to the region under the proposals. The decision has to be endorsed by the German Parliament, which could vote on it as early as tomorrow.

“That’s an enormous move,” declared Ms Davidson. “Even getting past the psyche of the lack of German interventionsm postwar, that is an enormous move and shows there is an absolute coalition of western civilised nations, who say you will not destroy a way of life; you will not wipe us off the planet, we will not allow you to do that.”

Asked if IS was an existential threat, Ms Davidson replied: “Yes I do.”

The Scots Tory leader made clear she did not criticise or condemn anyone who held a different view to her on Syria, stressing this was a complex issue.

“But when I hear people say we need to have a negotiated solution, a diplomatic solution, I wonder what that looks like when this is a state without borders; this is not a land dispute…This is an existential threat to the way of life of western democratic nations.”

She added this was “a time for serious, level-headed and responsible action and consideration. This is not taken lightly…This is a time for moral courage and genuine leadership, which is what the Prime Minister is showing”.