Don’t take this as gospel, but I’ve just asked about the token swap issue to a UK accountant that is more crypto savvy than most. This was his response:
"My view is that if you are being forced to exchange one crypto asset for the same one on a different network my inclination is that the nearest comparison would be a share for share for exchange as part of a company’s reorganisation.
In these circumstances, you wouldn’t usually expect a taxable event to arise.
Equally if bonus shares are issued as part of a company reorganisation you would not normally expect a taxable event to arise. Put very simply the original base cost of the shareholding would be diluted. I would argue that a similar situation would apply where a similar transaction happened in relation to a crypto holding."