Equity transfer (USC only) to joint ownership (USC + UKC)

I am a dual UK, accidental US citizen living in UK.

I bough an apartment with my wife, but because of age and affordability requirements we originally put the flat and mortgage in my name only.

Now we are coming to remortgage and we plan to do an equity transfer to put the house in joint names and have a mortgage jointly. I thought this is better going forward long term as I would only have US tax liabilities on my half of the property (e.g. at renouncement prior to retirement or on sale of the property).

Are there any consequences or reporting requirements for doing this? We have been paying the mortgage together and consider it shared over the whole time.

There will inevitably be a huge currency gain on refinancing.

There will inevitably be a huge currency gain on refinancing.

Could you unpack this a bit? I have no idea what you mean, or how it applies to my question about equity transfer to spouse.

With the mortgage market in the UK based around relatively short term products (2,5,10 years) refinancing is quite frequent.

I don't at the moment declare the value of my property anywhere in my tax return - should I?

If I understand to do thing properly (spouse is non-resident alien) I need to declare income gain on the half I transfer to her.

How do I do this?
Take the increase in the property price from what we paid to the new valuation, divide by 2 (the half I give her) and declare that as capital gains?
But how do I include the mortgage liability (that I actually own only a small fraction of the property).
Should I instead take the percetange I own now, calculate the gain on that percentage of the property, divide by 2 for the half I transfer, and then declare that as a capital gain?
It is only 2 years so any gain will be small so I would rather do it now than in the future.

Any advice appreciated.

The pond crashed after June 2016. Any refinancing today will result in a large currency gain on the mortgage debt. The gain is potentially taxable as ordinary income. The length of time is irrelevant - it is simply an issue of FOREX movement.

The current structure is unconventional; I'd suggest professional advice.