You might find the school holidays a tricky time to use the voucher. This is because BA may consider that demand is sufficiently high at this time that the expected revenue boost through making seats available for cash sales only outweighs the loyalty benefits of offering redemption seats.

However there are at least some flights open for rewards in the summer. For example you could burn a 2-4-1 on LHR<>SIN in Club World, outbound on 1st August and returning on 12th August.