The Government needs a "grand strategy" to defeat the Islamic State terror group, taking in measures to promote stability and reform in the Muslim world as well as military action in Iraq and Syria, a parliamentary committee has said.
The House of Commons Defence Committee said that the gains being made in the military campaign risk being "undermined" by a lack of progress on the political side.
UK and coalition strategy of eliminating IS - also known as Daesh, Isis and Isil - by taking its territory in western Iraq and northern Syria by military force is "necessary but not sufficient", the cross-party committee warned in a report,
Even if it is crushed in its current strongholds, the group or its affiliates could resurface in Africa or south-east Asia or be replaced in the Middle East by "other groups posing similar or even greater threats".
The committee warned that Western countries, including the UK, might find themselves faced with a choice between repressive dictators such as Syria's Bashar al-Assad or violent Islamist revolutionaries, and will have to make a "hard-headed evaluation of which of the unpalatable prospects poses the lesser threat to our national interests".
While the Government's long-term strategy of promoting a "stable, secure, democratic" future for the Middle East was "laudable", the report warned that it was "far from clear" whether the pro-democracy forces unleashed by the so-called Arab Spring of 2011 would be capable of fostering a transition to Western-style pluralist and tolerant systems.
There was no consensus on the true political or religious motivation of the supposedly "moderate" groups which the intervention in Syria was intended to support, it found.
And it said that, despite differences with Moscow, military co-operation with Assad-backing Russia "may be the only way in which Daesh can finally be suppressed or defeated in Syria".
The report detailed 550 airstrikes since December 2015 by British forces in Iraq, where it said coalition military effort was "bearing fruit".
But it warned that progress was "much less certain" in Syria, where a far lower tally of 65 strikes have been made, only a minority of which "appear to be in support of opposition forces on the ground".
Earlier Western interventions in countries such as Iraq, Afghanistan and Libya bore out the argument that it must be local forces - backed where necessary by coalition air power - which take and hold territory from insurgent groups such as IS, said the report.
But while there was evidence of this happening in Iraq, the air operations in Syria were being held back by "a lack of partners on the ground" who could capitalise on them, said the committee.
"Whilst the military effort in Iraq is bearing fruit, that is much less certain in Syria," said the committee. "We believe this is partly due to the aspirations of the UK Government in respect of each country.
"The goals in Iraq are to remove territory from Daesh, to strengthen the Iraqi Government and to maintain Iraq as a unitary state. The goals in Syria are not only to defeat Daesh, but also to help bring into being a government which will be neither authoritarian and repressive, on the one hand, nor Islamist and extreme, on the other. These goals cannot be accomplished by military means alone."
The disparity between the effort being put into military and stabilisation efforts was "concerning", said the committee, which added that the low priority being given to diplomatic and development work "does not reassure us about Iraq's long-term future".
The report warned: "Whilst the progress in the military campaign to counter Daesh is beginning to gain momentum, the same cannot be said for the progress of political reform. A lack of political reform in Iraq, let alone Syria, may well undermine the military progress to date, removing the threat of Daesh only for it to be replaced by other groups posing similar or even greater threats."
The committee said UK training missions in Iraq had been "effective and substantial", but it voiced "great concern" at delays in supplying ammunition for machine guns provided to Kurdish Peshmerga fighters.
It called on the Government to put more information about the targets for airstrikes in Syria into the public domain, in order to "justify and validate" its policy of military action.
A government spokesman said: "The UK is at the forefront of efforts to defeat Daesh in Iraq and Syria. We have conducted over 1,000 air strikes, which is second only to the US in both countries, and have helped train more than 25,000 Iraqi forces.
"As a result, Daesh is losing territory in Iraq and Syria. Daesh can't be defeated by military means alone, which is why our strategy tackles its finances, propaganda, flow of foreign fighters and evolving terrorist threat.
"We're supporting the Iraqi government to deliver stabilisation, reconciliation and reform, and are working with international partners and the UN towards a political settlement in Syria."