Adding a partner to a title deed

My partner has paid off the mortgage 40K and we want to add her to the title deeds. There is now no mortgage on the property but technically money has exchanged hands. We'd both like to now be on the deeds. We are not sure which application we need to add onto the AP1 form or what fee this would be. House is worth £250K approx from last valuation. Many thanks, Sally 

Sally - how to transfer the whole legal ownership from a sole to joint names is covered in a number of forum threads and our online guidance also explains what's needed - Registering land or property with HM Land Registry: Change the registered owner name - GOV.UK
You will need HMLR forms AP1, TR1 and ID1/ID3 as appropriate. Panel 4 of form AP1 can refer to "Transfer 1 to 2 - Full market value £250K'
The fee is a Scale 2 fee on half the current market value - HM Land Registry: Registration Services fees - GOV.UK