Good idea for a thread!
The Signal offer a lunchtime special menu - 2 courses for £10 (not on their website). It can be a bit hit and miss, but not bad value. It’s also not really two proper courses, as the starter is more like a side order, served at the same time. I think the choices vary week by week.
Tse’s (the Chinese restaurant by The Teapot) also offers a lunchtime deal. Can’t remember the details, but it’s soup or spring roll plus a main course for less than £10.