It's the usual scenario, the midlands breeds them, the south east gets them....we're a right bunch of total breeders...lol......the main reason showers are building in the south midlands towards you is that they are passing through areas of favourable development, ie convective energy, increased lift & solar heating....here in the NW midlands we have the first 2 ingredients, but a lack of solar heating due to dissipating anvil shields from showers/further north