It's definitely easier to not have a joint account. My husband and I keep our finances separate. I file my US tax return as married filing separately, and I only report my own accounts/details on FBAR each year.
As for filing FBAR, it's not just a single account balance. You trigger FBAR if the total of all of the foreign accounts that you have signatory authority on exceeds $10,000 at any point in the calendar year. So if you have a small joint account for paying your monthly bills in, and at the start of each month it has a high balance of £2000, and then you also have a savings and current account in just your name that reaches £5000 and £1100, respectively, in early December, that's a total of £8100 in foreign accounts, which is just over $10,000 at today's exchange rate, and you could have to file FBAR.