Short answer: sometimes, and finding out after the sign is up is the expensive way to learn.
Most standard fascia signs fall under "deemed consent" — you can put them up without a planning application, within limits. The limits are the trap. Illuminate the sign and the rules tighten. Go above 4.6 metres. Put it on a listed building or in a conservation area — and chunks of Stockport, Didsbury, Knutsford and half the towns we work in are conservation areas — and you need consent for things you'd never expect.
Councils do enforce this. I've seen a Bury shopkeeper ordered to strip out a brand-new illuminated sign because nobody checked. The sign was fine. The paperwork wasn't. That's £2,000 in the skip.
What actually triggers an application, roughly: internal or external illumination in sensitive areas, signs above first-floor level, projecting signs over a certain size, anything on listed premises, and digital or flashing displays almost everywhere. Static, unlit, sensibly sized fascia on a normal high street shop? Usually fine.
The cheap insurance: one phone call to the council's planning department before you order, with the sign drawing in front of you. Ten minutes. Or work with a signage designer who does the drawings to submission standard as part of the job — ours go out ready for planning when planning is needed.
Don't let a £150 admin step turn a £2,000 sign into landfill.