Uniqlo is the mutt's nuts. Their clobber is (mostly) great quality and dirt cheap. Their long johns are essential cold snap wear and I'm a particularly big fan of their well-cut shirts, which at £15-20 are bargain-tastic. At the mo, they have these awesome 'ugly' mixed pattern flannel shirts in.
For those wishing to spunk £143 rather than £15, R.Newbold do a sweet flannel shirt you can pick up at Goodhood.