Note: The first couple of times I tried to apply this deal I had received an error but on the 5th time it worked.
EE are offering an unlimited data add-on to existing customers for £25.
From what I can see, EE are offering unlimited 5G at £41 a month and I have personally been offered £20 a month for 100GB, so £5 extra for unlimited feels like a good deal.
This is of course on top of your existing plan. I'm current on £10 for 10GB (I don't often use much data).
Perhaps EE have a 4G unlimited data plan for cheaper I couldn't see but happy to be proved wrong.
Only came across this after moving property and needing a boost of data for 30 days while waiting for an internet installation.
Hope this is useful to someone Edit: It's possible based on what some commented have said that the unlimited data price may differ depending on how much you're paying for your contract.