APD has increased. As far as I know, reduced rate covers all of WT and ET. Standard covers WT+, CE, CW and First.

It is defined partially by seat pitch, so there may be exceptions:
Reduced rate - For travel in the lowest class of travel available on the plane for seat pitches less than 1.016 metres (40 inches).
Standard rate - For travel in any other class of travel or where the seat pitch is more than 1.016 metres (40 inches). Higher rate covers private jets.

Bands are given here. But briefly, A is 0 to 2,000 miles B is 2,001 miles to 5,500 miles and C over 5,500 miles. Connecting flights are treated as "one flight", where the highest class of service matters.

Headline is from 2024 to 2026 we'll see an APD increase across the board of roughly ~15%, unless you are flying in WT+, CE, CW and First internationally which sees a 25% increase.

Luckily it seems that Inverness and much of the Highlands are still immune from APD and on direct long-haul flights departing from airports in Northern Ireland (are there any?).

If a passenger pays to upgrade at any stage in the journey, then they’re travelling in the higher class. The same applies to free upgrades if there’s an element of entitlement or priority not enjoyed by other standard class passengers. For example ‘perks’ enjoyed by airline employees. A passenger remains in standard class if they get a free upgrade but has no expectation of, or entitlement to one. People who are escorts are exempt.