bewigged, I would follow this advice straight away to avoid further delays in dealing with your claim.
Write to or ring their complaints department (or even their underwriting department as they will be making the decision) and explain the situation. If they do then decide to void your policy (which I find highly unlikely), then you would need a ''final response'' from their complaints department (ie saying they will not overturn their decision) before you can take the case to the financial ombudsman service.
Quite honestly though, our underwriters would deal with this issue in a matter of days - it's normally just a case of updating the policy details, and as previously stated, it shouldn't even affect your premium.
In my dealing with Sabre, I've honestly found them to be useless - they seem to have no idea what they're doing.
I would also once again agree with chas - some of the stuff I've seen that has been ok'd by our underwriting to stay on cover is beyond, but we are very strict, and I'm not aware of all the criteria they have to adhere to.
I really wouldn't worry though