Jacket for office-corporate work and gym!

Hey guys, I need some advice. I’m working an entry-level corporate tech job in London and the dress code is business smart/casual. Most people wear shirts and trousers. It’s getting colder now and I’ve been layering with a jumper, but I want to buy a jacket that works for both the office and when I head to the gym after work. Basically something I can throw over my work clothes that doesn’t look out of place in the office, but also works over gym gear. Any suggestions?