See s.4 (and s.4A, but this was inserted by 1996 Act so is irrelevant to your query).
By s.4(3), "disposal" means creation or transfer of an estate or interest. I take this to demand a Deed rather than a contract; s.4Aproves my case, by applying s.4 to a contract (i.e. s.4 does not otherwise apply to a contract).
The Act does not directly link to LRA 2002, so it must be the date of the Deed (not registration of title) that counts.
JEFFREY SHAW, solicitor [and Topic Expert], Nether Edge Law*
1. Public advice is believed accurate, but I accept no legal responsibility except to direct-paying private clients.
2. Telephone advice: see http://www.landlordzone.co.uk/forums/showthread.php?t=34638.
3. For paid advice about conveyancing/leaseholds/L&T, contact me* and become a private client.
4. *- Contact info: click on my name (blue-highlight link).