You're assuming getting a mortgage (in the UK) is a click-click-approve process, but it is far from that
Purchasing any property is a many-month endeavour with solicitors/banks etc
Purchasing any property is a many-month endeavour with solicitors/banks etc
There are specialized firms w/ private capital that are happy to fund these midsize deal flow guys and finance them. Once you get a working relationship with a few such vendors it seems rather easy to get marginal deals done others would find impossible.
I don't know if this simply doesn't exist in the UK at all - but I'd bet money that it does in some form. Since bankers and finance make their money off the points on deployed capital, especially the loan officer making commission on the deal flow, the incentives are aligned to make more loans vs. less.
I think the hardest part of getting something like this going is the first 2 to 3 properties. After that and a few years of proven ability to manage cashflow here in the US your lending options open up exponentially both in number of lenders and the creative/exotic means of financing now available.