I would like to bring back my mountain bike to the UK. I will carry it in one of those bike bags. It weighs only about 10kgs.

My question is if I haven't brought it out with me will it be noticed on the way back?

It is well used so doesn't look new (liable for import tax) I could argue that I bought it out 6 years earlier even though I didn't.

I am worried as it cost me 125,000bht about 5 years ago so don't want it impounded...!

Any thoughts...?

Randy, I've just had a read of the HM Revenue site and it looks to me that it would be tax-free as personal effects under 4000 euros in value.
There is also another part that refers to moving your home to inside the EU that allows you to import your things tax-free as long as you've had them for more than six months.
http://customs.hmrc.gov.uk/channelsPortalWebApp/channelsPortalWebApp.portal?_nfpb=true&_pageLabel=pageLibrary_PublicNoticesAndInfoSheets&propertyType=document&columns=1&id=HMCE_CL_000282