you’re only a higher rate tax payer on the bit of money you pay over the rate.
lets say you earn 50k and the tax limit is 40k. (taking national insurance out for sake of ease) You are paying 40% tax on the last 10k – so £4k
if you salary sacrifice 10k into a pension/c2w (doesn’t matter which) – you will effectively have the full relief on that – so you would lose £6k from your take home pay, but gain £10k in pension/bikes (note : pension may be taxed when you withdraw it, and you might pay BIK on the bike at the end of the year).
if you salary sacrifice 15k, you would get the full 40% relief on the first 10k, then only 20% relief on the last 5k – so you would lose £10k from your take home pay, and gain £15k in pension/bikes.
On average, the latter case is ‘worse’ – but you’re not really losing anything from scenario 1 – its just that the additional benefit you’re getting from scrificing even more is less. You are still getting the full benefit on the 10k, but only the ‘reduced benefit’ on the 5k. you are not getting a reduced benefit on the full 15k
