If UK resident and get married in US is it legal UK?

The validity of a marriage in the UK depends on whether it was legally recognised in the jurisdiction where it took place, in this case the United States. Generally speaking, a marriage performed in a foreign country will be recognised in the UK if it was valid according to the laws of that country at the time it took place. So if you are a UK resident and got married in the US, your marriage will likely be considered legal in the UK as long as it met all the legal requirements for marriage in the US state where it was performed.

It's important to note that there may be specific requirements and procedures to follow in order to ensure your US marriage is recognised in the UK. These may include obtaining certain documents and having them legalised or apostilled, and possibly registering the marriage with the relevant authorities in the UK. You may want to consult with an attorney experienced in international family law or contact the UK government's Foreign, Commonwealth & Development Office (FCDO) for more detailed guidance on the specific requirements and processes involved in having a US marriage recognised in the UK.