You want to transfer an 8 foot palm from the US to London? I'm thinking of the logistics. Will be very stressful on the palm - no water or light for at least a week aside from being knocked around and having to adjust to a new circadian rhythm. Sounds expensive too; probably more than just buying a new palm tree in London when you get there.

I assume you're not actually in USA, despite the flag showing above your question. Either way, Kentia is not hardy outdoors in the UK, so if you do transfer it outdoors, be prepared for it to simply die as soon as the frosts arrive, though in a very mild winter with little frost, it may not die - it'll just look terrible by spring. As for sunlight, its best not to expose it to direct sun - these plants do perfectly well with reasonable to bright daylight conditions, and exposing it to direct sun now will cause it to suffer.
The sad fact is, they always do get too big for the average living room - mine's been out on the very large, indoor landing, outside my front door, where it can spread and grow to its heart's content, but if I ever move, it'll have to go unless I can find someone with an atrium and a large space to house it in.

I am guessing the plant is in your London home not in America. I have had some success planting houseplants in the garden. I just put them in the ground and hope for the best, if they don't survive it's no loss as I didn't want them in the house any longer. For the best chance of success I would put it out in early summer to give it plenty of time to establish itself before the winter.

Some companies that specialize in providing indoor plants for offices and malls might be interested in buying your palm. You will probably only get cents on the dollar (pence on the pound?) for it, but it wouldn't be wasted. I would start by searching "tropical plant stores", or asking the local garden centers.

Many buildings, hotels and restaurants in New York use full grown palms for indoor displays.