The document entitled Guidance on how Syrian nationals in the UK can extend their visa based on the concessions to the Immigration Rules was updated on 29 February 2016. Essentially, it allows Syrians in the UK as Tier 4 or short term students, family members of Points-Bused System migrants, visitors or overseas domestic workers to extend their leave in their existing category or to switch categories within the UK without having to apply for entry clearance. It also includes a helpful waiver on producing certain specified documents:

If the Secretary of State is satisfied that due to the civil unrest in Syria a required document under the immigration rules … cannot be obtained from Syria, the requirement to provide that document may be waived.

What the guidance does not say is that almost any Syrian would be entitled to asylum if they wished to make a claim, and that if a successful claim was made then he or she would be entitled to family reunion with any spouse or children still in Syria.

Source: Guidance for Syrian nationals in the UK on how to extend their visa – Publications – GOV.UK