Hobbs is good for smart dresses/jackets. If you have the patience to filter out all the Northern soul trouser suits and frilly polyester blouses, you can still get some nice things from M&S - but they are very well hidden among the weird stuff.
I buy good dresses from places like Warehouse and Closet and Oasis and team them with heels. Stylish without being frumpy - most can be worn with thicker tights in winter, or bare legs in summer. Tends to work out cheaper buying dresses than separates plus not many dresses need ironing!
Asos are great for bulk ordering brands and own label - real variety of prices too.
Zara are great for trendy pieces and have a huge range.
Gap are great for staple trousers and shirts.
M&S are great for staple shoes, but i'll be honest I spend all weekend in converse with the kids so i love the chance to put on a killer heel for work - I tend to splurge on a decent black pair from Kurt Geiger or Dune, then buy some funkier coloured shoes from new look or zara.
Agree on Hobbs and lk bennet. M&S and COS too. Buy 3 smart dresses (at least one navy / black) and 2 other and just wear them like a uniform. Add 1 or 2 others when you're flush. I've been down the route of cheaper alternatives and they don't stand up to multiple wears. A £160 dress from Hobbs is a terrifying thought particularly when you're on may leave and counting the pennies, but it will last you years when a £60 warehouse one will (usually) need to be in the bin after 3-4 months on a weekly wear basis.