As many US military sources now contend, did the British troops do a poor job in Iraq?

The British troops took part in an illegal invasion of a sovereign state. During their occupation of Basra, they engaged in the torture and killing of captives, allowed Shi'ite militias with close links to Iran to gain much control over Basra, and refrained from isting the nascent Iraqi army (isted by US troops) during the most heavy fighting. The infrastructure in Basra is still very much in disrepair and many US military sources now contend that the British troops were not as effective as they could have been. Can the British role in Iraq therefore be judged a success, as depicted by many British media outlets?