Waitrose usually have a good selection of sherries, particularly at the bigger stores and also in their Food Halls at the John Lewis stores on Oxford Street and Bluewater.

The Sampler, 266 Upper Street, Islington, London N1 2UQ
One of my favourite wine merchants, mainly because of the sampling machines but also because of their range of sherries. They have sherries from Valdespino and Equipo Navazos.

Bottle Apostle, 95 Lauriston Road,Victoria Park Village, London E9 7HJ

Lea & Sandeman, four shops in London and delivery UK-wide.