Single parent has had Housing Benefit suspended due to information received of them both working and having live in partner. Neither of which are true.
How long can the authority leave the HB in suspension without investigating that the claim is genuine?
Has the claimant any way of forcing the authority to reinstate the benefit until they have evidence to stop the benefit?

I stand to be corrected on this one but it is my understanding that there is no time limit and it really boils down to what is reasonable. My approach would be to write to the authority highlighting any evidence that counters the allegation. If the matter is not dealt with in a reasonable time frame threaten to make a formal complaint, if necessary to the LGO, your local MP might be interested as well. Judicial Review may be an option but you should try and obtain more info first about their decision to suspend benefit in the first place (also don't forget the 3 month time limit). A JR pre action protocol letter to the authority can often focus their minds, particulalry if client is entitled to Legal Aid and the LA know they will on to a hiding on costs.

If the HB dept have advised you why they have suspended the HB then they must be in a position to ask her in for an interview under caution. Any good fraud dept would gather evidence before suspending HB and then taking further action /interviewing under caution etc. It seems that they given away too much information to have much to go on for any further action as if these allegations are true, she has the chance to move the partner out /stop work etc.
I would suggest pushing the fraud section for an interview with your client where the allegations can be discussed in full and you can dispute their 'evidence'. Or perhaps offer to refer the case to the Ombudsmen -usually gets things moving!

You can, in fact, put considerable pressure on the LA to deal with this matter quickly and, on the presumption that you have authority from the client, can insist on an early hearing - but only by being a bully. Polite and firm don't work!

If you can force them into an early interview then they will have to present thier evidence because without knowing what that is, you really are on a loser.

Bear in mind that regardless of the "charges", they are not supposed to threaten her tenancy or put her in a situation where she could lose her home because of non-payment of rent. This is a good weapon - don't be afraid to use it. Delays in dealing with the matter come under that heading and yes, the Ombudsman is brilliant and it usually works but the bottom line is - find out what evidence they have and work from there.