There's a few good wine merchants in Scotland who I'd recommend popping into and asking the same question. Luvians in Cupar and St. Andrews and Raeburns in Edinburgh. Both have tremendous selections and are a world away from supermarket fodder. There's also a spanish specialist who I think are called Moreno wines and based in England.
In general, strong fruity reds shouts Australia and in particular South Australia (Barossa Valley, McClaren Vale, etc).
Reds from Puglia in Italy often have a lot of stuffing (but also some complexity) for the price. Ditto Sicily.
Various other Spanish regions might offer interest e.g. Penedes. For a wine at just short of £20 that might match your preferences, try Coma Velha by Mas D'en Gil. Waitrose stock it in the inner cellar, but a few independant merchants also stock it. It's possible to get it for as cheap as £15 if you strike it lucky.
Chile is good for clean cheap fruity reds, which only really lack for complexity and cellaring potential, but at the price are very good
There's basically a whole world of wine out there - all I'd say is taste as much as you can and you'll start to identify your palate preferences.
Best of luck