You can only get tax relief on the actual tax paid. You'll either get it back on the medical expenses or the AVC or both if you have enough paid. So go ahead and do your medical expenses claim. I do mine in Jan every year, then when I get my utility bills I go back in and claim remote working relief, then if needed an AVC. No issue getting multiple Statements of Liability issued. And you can go back up to 4 years for any unclaimed medical expenses too.