Britain is playing a prominent political and diplomatic role over Libya but a remarkably modest one in the military campaign, an initial analysis of available information of the first week's action suggests.

The Ministry of Defence, in marked contrast to the Pentagon and the French armed forces, declines to say how many bombs or missiles have been fired from RAF Tornados or how many Tomahawk cruise missiles have been fired from HMS Triumph (a Trafalgar-class submarine which the MoD declined to identify until David Cameron named her in the Commons).

However, defence sources say a total of seven Tomahawk cruise missiles have been fired from Triumph, compared to at least 168 fired from US submarines and ships.

Liam Fox, the defence secretary, said Tornado aircraft on Thursday launched "a number of guided Brimstone missiles at Libyan armoured vehicles which were threatening the civilian population of Ajdabiya".

He described Brimstone as a "high-precision, low collateral damage weapon optimised against demanding and mobile targets".

Four Libyan tanks with their guns facing Ajdabiya were destroyed by Brimstone missiles, Major General John Lorimer, Britain's chief military spokesman, said later on Friday. Three other tanks nearby were hit by missiles fired from French or US planes.

One of three Tomahawk cruise missiles fired on Sunday night got stuck in the submarine's launch tube, it emerged.

This was the first time the Tornados – whose home base is RAF Marham in Norfolk but which now fly from the southern Italian base of Gioia del Colle – had fired weapons at Libyan targets since Saturday, the first night of the campaign. Four Tornados were involved, probably firing no more than two bombs or Storm Shadow missiles each.

The following night, the Tornados' bombing run was aborted because a number of civilians, later identified as including western journalists, were found to be in the "intended target area", the MoD has said.

It is possible that no more than about eight bombs or missiles had been fired from RAF Tornados before the Brimstone attacks on Thursday night. That contrasts with hundreds of attacks by US and French aircraft, with, in one reported incident, US planes firing 40 missiles at one Libyan air base.

A total of eight RAF Tornados and 10 Typhoons are involved in the conflict.

William Hague, the foreign secretary, said on Thursday that the RAF had flown 59 missions over Libya. The large majority have been reconnaissance missions. They have also included what the MoD emphasises were the first Eurofighter/Typhoon aircraft deployed in what it described as "hostile airspace".

The 10 Typhoons are only suitable for air-to-air combat, according to the MoD. The ground attack version apparently is not ready to take over the Tornados' role – though defence sources point out that the high profile the Tornados are enjoying will make it much harder for the government to scrap them as soon as it would otherwise like to.

The RAF is responsible for policing the "no-fly zone" over eastern Libya, the rebel stronghold. Actively engaged in Afghanistan, it does not have any more aircraft available to take part in the Libyan operations.