Are the roles of "Shadow Home Secretary" ... etc official? If the Polls are to be believed, then it would appear Reform have as much or even more "right" to assume these titles as (say) the Conservatives.
Yes, official, with associated salaries, 'His Majesty's Opposition' (HMO) being based on number of parliamentary seats, not opinion polls. I'm not sure what would happen to the designation if the number of seats were to change sufficiently in between elections to change the largest opposition party in terms of seats.
Farage is desperate for Reform to be viewed as HMO, but it's not.