Ok, I wanted to transfer a domain from Fasthosts.co.uk TO Namecheap.com. I typed in 'NAMECHEAP' as the IPS tag, and then when I visited Namecheap, they said the IPS tag must be 'ENOM'.
'ENOM' is the company that handles their transfers. So now.. the domain has been removed off my Fasthosts account - and the domain is 'stuck' as it can't be transferred to Namecheap..

Do I have to contact either registrars or something?

Contact Nominet or go to http://www.nominet.org.uk and try to login to your account (if you havent done this before, as long as your email address is the admin one you can request a lost password) then you can log in.

At least you have some control over it if you need to change nameservers, then on Monday contact Nominet +44 1865 332211 and go through to registrant services, they will normally charge you £11.50 for the pleasure.

That or transfer it to someone who is actually a Nominet Member/Registrar.

I've said this here many times before (and I know that not everybody agrees) - but as a UK resident you really should think twice before transferring a .uk domain to a non-UK registrar.

The .uk system in fundamentally different from the GTLD world. When you register a .com you enter into a contract with your registrar and that's it. When you register a .uk you and your registrar separately enter into a contract with Nominet (the registry). If your registrar is outside the UK things can get quite messy contract-wise as you have three separate contracts two of which are under UK law and one of which is under the law of the registrar's country. Also, I've found that by and large non-UK registrars don't understand the intricacies of the .uk system.

In your case things are going to be even more messy because you are moving to a non-UK reseller of a non-UK registrar.

I wouldn't.

But if you want to continue to go down this road then, as suggested by the previous poster, you need to sort it out direct with Nominet. You should already have an account with them (though you may not be aware of it). As long as your admin contact address is up to date they should just re-send you your log-in details and then you will be able to sort the tag change from there. If your admin contact address is not up to date then you will have to go through some hoops and pay a fee, but as long as the domain is registered in your name it should be fairly straightforward.

Just for the record, NetEarth UK Ltd is the Nominet member and our UK nominet TAG has been in use since 1997, NetEarth One also has a seperate TAG although both are registered to NetEarth UK Ltd for the avoidance of any doubt.

So now.. the domain has been removed off my Fasthosts account - and the domain is 'stuck' as it can't be transferred to Namecheap..

You need to login to the Nominet online service at www.nic.uk
pay the £10+vat TAG change fee and re-tag it to the correct IPS-Key.
Seems odd moving from a German *registrar* (FH=1und1) to a US *reseller* for a .uk domain ...

Seems odd moving from a German *registrar* (FH=1und1) to a US *reseller* for a .uk domain ...

While FH is now under German ownership it remains a UK limited company, with all contracts under UK not German law.