Big question is do you want the modem/router all in one box, or are you planning to continue to use the white Openreach modem.
If using the white modem then:
Within £50 budget it is really TP-Link
TP-Link for £40
Offers dual-band and should be fine for FTTC type speeds, though would normally suggest the WDR4300 or the Archer units but you are heading more towards Asus pricing. Asus has a much better GUI on the router.
A popular choice at £95 is the Asus RT-N66U
runs Asus firmware, or a variety of DD-WRT versions to let you do more stuff with the router. If white hardware is your preference there is a £5 cheaper version on Amazon.
Latest AC Wireless for £120 in Asus RT-AC66U
A little more speed and USB 3.0 device support for £155 Asus RT-AC68U