I am 99% sure that is illegal. You have no legal obligation to claim sanctuary in the first safe country you find. Declining birth rates are normal in successful nations - and immigration helps balance that out.I think Reform would reject asylum requests for anyone arriving from a safe country, which would cover the large majority. Is that illegal? Not even sure myself. I don't think it is the only issue facing this country, but it is a big one and, depending on where you live, it is very easy to see the negatives first hand. Other, much larger problems, such as the declining birth rate and the ageing population with spiralling cost of care for the elderly just aren't as easy to campaign on because they aren't as obviously visible.
The whole thing is hyperbole and stupidity.