Safe way to fill existing standard LPG Gas

Tried desperately to define a heading in 50 characters without drawing in the usual 'trolls' extolling rules and regulations etc etc. but here goes:

In view of the rising real cost of bottled gas 'v' LPG sold through pumps, is it possible to reload from LPG garage forecourts and existing standard gas bottles by way of a safe and certified adaptor?

The object is to reduce the cost to refill without having the outlay of refillable bottle as I can't/won't fit permanently to my caravan. 

I seem to recall previous posts around it being possible on the continent via website purchases of the adaptors and would welcome information on the possibility.

Please try to refrain from opinions on the rights and wrongs of the potential dangers etc etc as these have been covered very well in posts around the refillable cylinders discussions.  I would hope most are also aware that the UK garages have a dislike of filling refillable gas bottles not permanently fitted to the vehicle.