It is recommended to apply for a visitor visa in advance of travel to the UK if you have any adverse UK immigration history.
It's not a set-in-stone rule that you must, and you can take your chances without one, but it is usually a good idea as you'll have peace of mind that you won't run into problems at the border if you show up without prior entry clearance, and will ensure that you don't lose the cost of your flight ticket(s) should you be bounced again.