It depends on your body shape etc, but how about some simple black skinny or drainpipe fit trousers (M&S have some nice ones for £19.50) with a white or cream simple top or blouse? Accessorise with a big bold necklace and stud earrings in a similar colour. Smart watch and a bangle or 2.
The drainpipe (if so I would recommend getting ankle grazer length) trousers from m and s with light blouse as suggested by catsriding would look great.
If you aren't comfy with tight trousers, a wrap dress with black tights and plain heels or flats would look great with an hourglass figure. If cold just add a lightweight cardigan. I've seen lovely wrap type dresses in places like new look, matalan and Asda for very reasonable prices. Can't go wrong with dress and tights for office based interviews!
Google smartworks.org - dedicated to helping women get back into work after a break and they offer practical help to overcome outfit and confidence worries. Not sure if there's one near you or if it's quite right for you personal but seems like a great idea for so many in a similar situation