I'm a US citizen and I work for a US company. My company has a subsidiary in the UK where we have at least one person employed.

What are my options for working from London? How long can a "business" trip to the UK last? And how frequently can I do it?

Also, what would be the process of me transferring to the UK subsidiary? I believe there is an easier visa process for an internal company transfer but I'm not sure where to start looking for that.

Thank you!