one pair footwear (boots/shoes as you like but keep them polished and looked after)
one smartish jacket (not part of suit)
two smartish trousers
four or five tops (wear s/s ones when it's hot, l/s if cold, l/s w vest if arctic)
scarf/wrap thing (carry instead of jacket when hot, add to jacket when cold)
I don't wear black (and am evangelical about getting others to stop, it's so unimaginative), so if this was me picking from clothes I've actually got I'd do:
tan low-heeled boots
cream linen/cotton jacket
one pair chocolate brown trous
one pair tan trous
cotton tops with flattering necklines in
brown s/s
brown l/s
terracotta 3/4 s
olive green 3/4 s
one cream blouse in case need to be v formal
orange patterned scarf
but there's nothing to stop you getting black shoes/trous/jacket/scarf and coloured tops, or whatever colour combo you like.
To get this for £50 and have it all fit and last is a bit beyond me tbh - I'd normally spend that much on just the boots and make them last five years . Everywhere has sales on at the moment though, and if you go with a strict list you may find some bargains.
Primark, Peacocks, Matalan etc are good for cotton tops and blouses, and you might get lucky with trousers and jackets if you're the right shape.
I really wouldn't skimp on footwear though - non-leather boots with cheap heels never seem to last that well, and they've got to be comfy if you're running round all day.
Don't forget nice bag you can keep all your stuff in - armfuls of papers dropping everywhere never a good look. And if it matches your shoes so much the better .