So I bought an MRP triple bash guard but need to enlarge the hole in middle of it to have it slide over the BB shell (on a Zesty) so I can fasten to the ISCG tabs. I tried an old file I had lying around and it seemed a lot of effort for a tiny bit of metal removed (mostly the anodising :p ).
I've been looking for a drill bit that would do the job but can't see anything obvious (only needs about 0.5mm removed around the circumference). B&Q stock this for a Dremel (which I don't own) http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_secondid=9288328&fh_view_size=10&fh_start_index=20&fh_eds=%3f&fh_location=//catalog01/en_GB/categories&lt;{9372015}/categories<{9372047}/categories<{9372205}&fh_refview=lister&ts=1251212260754&isSearch=false

could I just use that in a drill or is something likely to kill me?
I suck at DIY and also don't want to spend more than a few quid as it's a one-time deal, any other ideas if the thing in the link wouldn't work?

You could try a tapered hole cutter

Just file it with a round file being careful to cover all areas equally (draw on your limits in pen), anything you might be able to buy will take more cash than you're willing to spare.

battery dremel at lidl or aldi recently for £25 quid with all the tools think it was aldi.

I'll look out for you on the next series of BizarreER 🙂

If your only taking 0.5mm off, how about a long thin piece of wet-n-dry & take it off the BB shell instead…

tapered hole cutter is the tool for the job, maybe take it to a local small engineering firm and get them to do it. 2mins with proper tools.

[edited cos i didnt read the OP]

Yeah…………take it to a local engineering firm who will do a decent job in 2 minutes & won't charge a lot – if anything. Take along a bag of doughnuts to get them on side.

Will be a much better result than you filing at it for 30 mins and ending up with something roughly oval that looks absolute toilet. No offence meant, but without the correct tools metal is pretty hard & circles aren't easy to achieve!