There is also Arrow5, also SOuthampton, who is closely associated with Autolinkuk
Close to you in Poole is:
There is this thread, but its not been updated in a while:
You should also check the front chassis legs for rust at the same time, and take a decision. Its all very much fixable, but depends on your budget.
Repairing the sills to get a fresh MOT pass isn’t hard or expensive, and doesn’t need a specialist. Repairing it so its looks good cosmetically is another matter, and the costs can mount up.