Hi Morecoffee,
Excellent responses so far!
It'll all depend on the industry sector, your skills and experience along with if your field is one which is in high demand in the UK. Only a relative handful of employers want to hire from abroad due to all the increased workload to achieve it and the higher costs incurred to do so.
As mentioned by Aquila, it's not impossible, but it's very difficult if you wish to secure a job from the US. If you are in such an industry that often does recruit from outside the UK/EU, then look to jobs where the employer is asking for such. If your skillset/experience and industry sector is one where there's plenty of local potential candidates, then you'll find it very difficult to secure a firm job offer from the US and you'll need to re-evaluate your strategy for finding a job.
Cheers, DtM! West London & Slough UK!