A note on the black street shoes for the milonga: While this might be standard for the milongueros it is not something i would recommend to anybody who dances even a tiny bit more modern. If the leader dances anything with foot-on-foot contact - sandwiches, drags, stops and so on it is much more comfortable for the follower if the leaders shoe does not have a welt. This is not a problem for followers - womens shoes are almost never welted - but the majority of mens shoes are. Gssh
I agree that in the UK it's difficult to find appropriate street shoes and that they should be non-welted. Welted shoes are too heavy and clumsy. The change in shoe style over the years has affected the choice we have but a street shoe, carefully chosen, is effective for social (milonguero?) tango. The "correct" shoe should add to the feel, stability and dynamics of the dance and a typical dance shoe doesn't do that in the same way.
First of all sorry for the late reply and welcome on the board. You surf the internet for a good online shoe store.