There are some amazingly good US tax advisers based in the United States. However, hiring a tax adviser outside of the United Kingdom presents unique issues:
1. Someone in the States is unlikely to be dual US/UK qualified, so may overlook important UK tax planning opportunities, possibly costing more tax than necessary.
2. If something goes wrong, you'd have to sue in the State where the business is based, this could be expensive when it would be simpler and cheaper to sue in the British Courts
3. If something goes wrong there is no local UK professional body you could complain to.
4. Someone in the US would not be subject to UK anti-money laundering rules, which exist to protect the consumer. This adds risk because advisers in the US are not required to undertake the same levels of due diligence as advisers throughout the EU.
5. Time zones and paying in non-Sterling currencies may add difficulty for some folks.
Overall my experience is that using a dual US/UK qualified adviser is most prudent, but as I said above may well not suit everyone.