I thought that this type of repair was being used less frequently now. As far as I know, it is done to prolong the life of the road surface so as to reduce overall maintenance costs. It seems to consist of spreading a thin layer of molten tar over the road then scattering stone chips across it and letting the tar set with the stones embedded. As you have discovered, they don't all stick and large quantities of loose gravel end up being cleared by vehicles using the road.
I know a number of people who have had various types of damage caused by this practice. It's not helped by the fact that there is usually some @rse who thinks the recommended very low speed limit applied in these circumstances does not apply to him!
In my opinion, this shoddy form of road maintenance is dangerous and costly to many motorists and should be banned. The Highways Agency and local councils should be forced to make proper repairs and maintain all roads properly. After all, we all pay more than enough every year for our road fund licence - I thought this was supposed to be used to fund road maintenance.