Request Recommendation for ISDN Service in London UK

My apologies for the non-operational nature of this query. Please respond to tmckee@sdnglobal.com so that we can keep non-relevant messages off the list. I have need of a recommendation for an ISDN PRI provider in my Telecity Sovereign House colo (London UK). Also, it has been quite a while since I have dealt with ISDN RAS and need an experienced engineer on the ground to work with installation and configuration of the service. Any and all recommendations will be greatly appreciated. Tim McKee