Let me get this straight for myself...
You had NTL broadband installed, but you have a poo TV aerial, so the engineer nicely split the incoming NTL signal and plugged it into your 2 TVs allowing you to get clear channels 1 > 5.
NTL's area is bordering on the wall between your house and next door so you can get NTL no problems, but the physical cabling wont go to next door as it is outside of an NTL area? Therefore, the NTL engineer who installed their modem split the line going to your house off into theirs to stretch the boundary by 1 property?
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I would get a router and share 1 connection between the two of you - would certainly make sense to do so and it could resolve future problems with engineers raising eyebrows at how your incoming cable is split. I mean, it has been done genuinely as a favour by an engineer for you to receive a clear terrestrial signal on your TV but any future engineers may not choose to do it themselves and may think its a bodged up home job with a nicked modem or something. Plus it'd work out cheaper too
