Try LON-PZE by sleeper train - no tier points but a flat bed and one of the most beautiful stretches of railway anywhere in the world as you come into Penzance...
I agree, without a connecting LHR-NQY flight i would choose this option if my flight arrived into LHR at a suitable time of day, however i very much doubt if the OPs transatlantic will arrive at a suitable time to do this.
Interesting to note that the sleeper service is going to be protected under the bidding for the new great western franchise
cs