Sorry I don't think the slow responses are due to ntl, and the fact that other customers on that provider using the 'nicer' transits seeing slower responses indicates this.
The ping differences could just be different routes being taken along the fibre rings across the atlantic in the case of Tiscali.
That said there is some routing weirdness on ntl's network which I've documented elsewhere as yet to no response.
It does give the impression that ntl's 'MPLS' network is being configured manually
BTW Chrysalis why are you complaining about 125ms from Texas and ~80 from New York? I mean wtf dude?