I had virtually the same problem as India Four Two a while back, towing a Skylark 4 glider out of Nympsfield (Bristol Gliding Club) with a Jackaroo (4 seat Tiger Moth conversion, for those too young to remember) at a competition.
At about 100 ft over the edge of the airfield, crossing the ridge, a significant bit of turbulence must have displaced some trapped water, asi flickered and dropped to zero. It would have been unsociable to dump the glider, and unnecessary - I carried on with the tow (and subsequent circuit) on attitude and power, and parked while disconnecting the pitot and static lines and blowing out the water.
I declined the offer to carry on towing before fixing the problem, and the competition director quite understood my point of view.