Hi, my husband and I are now living in the UK but originally from Canada.
Before we moved here, my husband was working for the same company but he was doing field work as a geophysicist. He was paid in Canadian dollars in his Canadian bank account from his UK employer. He was paying Canadian taxes only as he was a Canadian resident and was not entitle to any of the benefits of being a UK resident (health insurance, pension, etc...) even if he worked in the office in Cambridge a few weeks yearly. He didn't need a visa to come to work in the UK as it was for short periods of time only (one month max at a time). His company was paying for a private medical insurance while he was out of Canada . I don't know if American citizen needs visa to visit in the UK, but Canadians don't if it's for short periods. You should be able to find more info on the British High Commision in the USA. It should be a lot easier than what you were expecting, especially if your company can pay you in USD. Hope this helps. don't hesitate if you have any more questions or are unsure about my explanations... Good luck