Hi JinJin,
I used to work in my IT career for 3 US companies with offices here in London. One of them was a large player and purchased a Law Practice Management company based out of Tallahassee called CMS Open and I often spoke with lawyers, solicitors, legal specialists etc. Some of my friends are lawyers here, some relatives as well. In the US, amongst my extended family, there's a number of lawyers too.
There'll always be a demand for legal specialists, however, here in the UK, there's now a level of over saturation and for a good many lawyers, the long term outlook is more bleak. On top of that, the pay levels aren't as good as they once were. If you are lucky and do get into a well established practice then don't get me wrong, you'll get a good salary and benefits package etc.
Due to the above, I'd say by moving here you'll need to keep your options open and realize that you may not get a job in your specific legal sector. London has the most concentrated law firms, so your best chance would be moving to someplace close to the Square Mile (name given to the part of the city with many law firms etc). There are of course other cities with law firms too but not as many as London.
Other jobs are available out of your sector, just be prepared to 'dumb down' your C.V/Resume in order to perhaps get them to talk with you and again, depending on what it is.
Look into if you can move here and get the required permissions that allow you to work. One of the more knowledgeable members on the forum can confirm maybe if then you are allowed to open up your own company and provide legal advice given your expetise. It might well mean that even though you are here, you could still 'operate' in NYC via your website etc. I'm not 100% sure on the above, just an idea really.
Else, discuss with your other half and I'd tentatively suggest that you move him/her over to the USA instead?
Cheers, DtM ! West London & Slough UK!