Transit times to London
Being not a pilot myself, but a bit of a transport anorak, and noting Piccadilly being the venue for the meeting, you may want to factor in the transit times, and if you are not already, make sure you have onward transport laid on - particularly if you are coming into Biggin. I am told it is important to get someone who knows the back roads into London from Biggin.
Equally, Luton to Piccadilly is straight forward - apart from the last bit. I am sure the FBO you use will have a deal with a chauffeur drive and I would have thought that is money we spent.
Hope I am not stating the obvious for you professional guys here - in fact it would be interesting to know how involved you would normally get in ensuring a smooth transition from aircraft to final destination.
Cheers
Mark