Stop me before I do something really stupid

My bike has a 130mm spacing between the dropouts, was thinking of getting a disc brake hub with a bolt on cog from london fixie bike shop, this is mainly because seems easy to set up, and easy to swap cog sizes. if i buy one for a 135mm spacing will i have any problems, i presume just few mm of axle stick out to the side?

I have 130mm rear spacing on my Raleigh, but for some reason measured it as 135mm when I was buying my wheel. As a result, I'm running a 135mm hub on the rear, but it hasn't caused me any huge problems. It does affect the chainline and I do notice more noise than on friends' bikes who have 130mm hubs, but I wouldn't lose any sleep over it. It'll be a bit of a tight fit, but you won't need to 'cold set' (i.e. bend) the frame to get it in - just wiggle it around a bit. As has been said - only do this on a steel frame, or you may be finding out first hand what the words 'catastrophic' and 'failure' mean.

If your rear spacing is 130mm though, and you can get a 130mm hub, then you should get a 130mm hub. I can't see the benefit in getting a disc brake hub on the rear over a standard track hub/fixed hub, but each to their own and everything... I got my wheel from On-One for about £70 IIRC and it's double fixed - just as easy to swap as undoing your locknuts, unbolting a cog and bolting another one on.

Now the Mercian I've just bought has 115mm rear dropouts - I'm thinking it's not the best idea to try and force a 135mm in there...