Henson left the Blues towards the end of last season's RaboDirect PRO12 after being dismissed for an alcohol-fuelled incident on the return journey from Glasgow.
It is not the first time that Henson- who made six appearances in the RaboDirect PRO12 last term - has left a club under a cloud following incidents at Toulon and Saracens.
But London Welsh coach Lyn Jones has seen Henson's best side when he coached him at the Ospreys and believes the 2005 and 2008 Grand Slam winner can still deliver on the pitch.
He said: "Gavin has a great talent but over the past three or four seasons he has not realised his full potential for a number of reasons that are well documented.
"What's important for Gavin is that he concentrates 100% on his game and learning how to become the best he can possibly be again. I think he can add a great deal to our game and we can also do a lot for him.
"We all appreciate the skills that he can bring to a game but what team-mates and coaches will be looking for is consistency of that ability.
"That's the challenge for Gavin, to hold his concentration fully on rugby as he did when he started his career, when rugby was first, second and third on his list of priorities."
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