"things can only get better" wasn't a labour anthem per-se but a song that D-Ream founder Peter Cunnah allowed the labour party to use as part of their 1997 campaign. but it was a very different labour party then, and Mr Blair was probably more rightwards leaning than David Cameron in 2010. Peter Cunnah later expressed misgivings about allowing his work to be politicised. whilst D-Ream's most famous member was physicist Brian Cox, he didn't play on "things can only get better", and his attitude to Brexit definitely doesn't match that of the current labour leadership, so it's doubtful whether this anthem will ever apply to labour again.