The GARDENA gardening expert
Dear Mr. W., the situation as you depict it is certainly a most annoying occurrence. As you know, I think nothing of apparent aids against pests which are nothing more than a waste of money. However, in the case of denaturants against moles, I am convinced of the efficacy of products which contain lemon oil as an active ingredient, because the animals definitely do not like the smell and are repelled by it.
However, I have three points to make: Firstly, you may have to apply the preparation across your 500 m² meadow and in the numerous mole tunnels to a comprehensive enough scope, and possibly repeatedly, so that the inconvenience for the animals is large enough to drive them off.
Secondly; are you sure that you weren't in fact successful, and that the empty mole tunnels have been settled into by a new influx of moles? And thirdly, it is important that you destroy the tunnels as soon as the moles have vacated them. Otherwise, the danger is that root voles will take over these tunnels (particularly in rural areas). They like to save themselves the work and move into mole tunnels.
In answer to your other question, dear Mr W., in winter, moles do continue to dig.