we have been advised have lhaso apso is the ideal breed for families with a person with an allergy,if this is correct is there a rescue centre to rehome such dogs ? if not where would we find one in east sussex/

It depends what the person is allergic to. If it's hair, then there are many non-moulting breeds which may be suitable. However it's more likely to be the dander or saliva which causes the allergic reaction - and all breeds have those! There's lots of information on the net about dogs and allergies (here's just one site); your best bet is to consider all the breeds then go and visit a breeder with adults, spending a couple of hours in the house, to see if they cause a reaction.