A good number of my clients are US citizens working in the UK or the other way around as UK citizens working in the USA.
I am sure it must be easier for you to work with one adviser who has experience of both tax systems and this is why I also prepare US tax returns alongside UK tax returns. This is particularly helpful if you need to take advantage of the US / UK tax treaty to help eliminate double taxation or the US foreign earned-income exclusion.
My fees are generally the same or slightly higher for US returns but the service quality remains the same and if available I can help you file your tax return to the IRS electronically or by post.
As always just drop me a short note for a brief conversation to see if I can help you.