Put your number into this:
http://www.prodigynet.co.uk/menu.php?page=support/adsllinecheck
Make sure it doesn't say anything about LLU, as if it does, the ISP you are migrating to will likely want to charge you for the migration, even though it may appear that you are on IPStream.
I am a Tiscali user on IPStream and because someone or something touched my line or records I was asked to pay a migration fee to join an IPStream provider, if I had used that checker and trusted it I would have avoided that complication so I just pass that advice on to you
Aside from the providers listed, UKFSN, ADSL24 and Vivaciti are part of the Enta.net resellers group and as far as I am aware you wont get a service that provides the highly reliable pings that Enta.net services do for the same price, whilst still retaining a usage limit of 30gb peak/300gb off peak, so I would investigate them if Gaming is important to you.