Britain is at the forefront of international efforts to topple the legitimate government of President Bashar al-Assad, and has promised to supply foreign backed terrorist groups with equipment to resume their attacks against army forces.

But in his interview with the Telegraph, the 61-year-old general warned of the consequences of a no-fly zone.

"If you wanted to have the material impact on the Syrian regime's calculations that some people seek, a no fly zone per-se is insufficient," he said.

"You have to be able, as we did successfully in Libya, to hit ground targets. You have to take out their air defenses.

"If you want to have the material effect that people seek you have to be able to hit ground targets and so you would be going to war if that is what you want to do," he added.

A lack of international consensus and the splintered nature of foreign backed terrorist groups made it difficult to forge a military solution, he said.

Richards retires on Thursday after a military career spanning more than 40 years.

British Foreign Secretary William Hague has promised lawmakers that the government would seek parliament's consent before deciding to arm the militant groups.

There has been overall concern that the weapons would certainly fall into the hands of terrorist groups.

Prime Minister David Cameron said last month, however, that the government reserved the right to intervene in Syria if it felt Britain's national interests were under threat.

NJF/NJF