By which legal authority does UK special forces have to be in Syria?

[Splott Dave]

The UK ground troops in Syria comes from a BBC article. As Splotty doesn't believe a word the BBC says, how come this is different?

Multiple sources have quoted it TB. The point being is that we have no right to be there. It's an incursion into a sovereign territory. It's not like it was some kind of hot pursuit from Jordan across poorly defined border regions in the desert.

We are aiding Jihadists against the legitimate government of Syria. What if the Syrian government started to aid terrorists who wanted to carry out attacks in Britain by way of retaliation?