Coventry Grinders is good for silver steel rod and ground gauge plate. Good service and very reasonable too, still cheaper than the usual 'model engineer' suppliers despite their P&P being a little higher.
I have used K-Steels in Huddersfield too who were very helpful and reasonable for noggins and heavy off-cuts in the past but I don't think they do mail order, although I could be wrong. I tended not to buy MS stock in dribs and drabs when acquiring materials. Why buy a 2ft length of rod from an ME supplier when you can buy a 3 metre length for nearly the same price from a local steel stock-holder and you have then got almost a lifetime's supply. You can cut it into 2ft lengths yourself if that's what you want.