Polar fleece is not antron fleece and it's not really similar, although many people make puppets out of it and it works just fine. Antron fleece - which a lot of people make a big deal about - really only needs to be used to make puppets for television so that seams are concealed. It's expensive and not really necessary if you're making puppets for theatre or live shows.
You can order antron through
Georgia Stage in the U.S., but it will probably be very expensive. In addition to shipping costs, you have to pay a tariff on it because it's a textile. I've heard that the UK tax on imported textiles is about 100% (they double the price) but maybe check with Kathy at G.S. and see if she knows whether or not that is true.
There are no UK suppliers for antron fleece unless you happen to find a puppet builder or someone else who is selling some that they've ordered. A good group to contact if you need to know where to get supplies is the
British Puppet & Model Theatre Guild. If you post an ad on their
message board you might get some helpful suggestions about where to find supplies locally.