I assume this stems from the case off Grange last year where the father and son were stuck and disorientated? The way the scenario is described in the post, I would say almost certainly not - dangerous and daft indeed, if one goes down the route of searching on instruments; that puts us beyond the "acceptable risk" approach and into sacrificing the crew for little chance of success. It's very rarely that the conditions are such that the fog is dense enough to get the person in trouble but shallow enough to get safely overhead.
Hummingfrog - none of us would rather go after speeders than help someone in distress, that one was done to death in September.
The problem is that with proper [2 pilot, IFR, winch etc etc] SAR assets spread thinly and police ASUs able to respond within minutes to most areas, we are potentially first on the scene of all these cases.
Standto - I'd caution against the capability of the crew. Police crews, regardless of their abilities,do not routinely train for this sort of thing.
In most cases, people have bust the rules and got the right result, trebles all round and nothing more said. As we all know however, the assessment after the event is based on the outcome. So far all the high profile UK cases have gone well but police crews are in an unenviable position, faced with not carrying out a duty of care on one hand and being accused of endangerment on the other.