Probably wasn't NTL themselves. The node-names of all braodband NTL customers look like they belong to 'head office'.
I am a NTL customer (broadband) and my firewall is hit frequently (mostly by other NTL subscribers). Most of the time it is either 'seek-and-display' robots looking for websites, or naughty boys trying to hook in with SUB-7 trojan or Unix RPC.
If most of that went overhead like something large and noisy on full chat, the short version is not to worry unless a) the b****r is hitting you several time a minutes or b) your firewall is not secure
[Edited for typo]
[ 06 November 2001: Message edited by: Sir_Lurkalot ]