Headlamp recommendations

It will be used for confined spaces and arms-length working mostly.
It must be USB chargeable. Budget is around £80 (€120)

There are the only three givens, all the rest is secondary.

I have looked at the Lensor H7R
Pros: adjustable
Cons: unregulated, batteries get poor reviews

and the New Petal Tikka R+
Pros: Familiar with Petal, It's own battery and charge indicator
Cons: not sure I want to be reactive. I have a distrust of helpful computers.

Diamond ReVolt
Pros: cheap and cheerful
Con: Cheap and cheerful, hideous.

Would you like USB chargeable that precludes you from using the light while you charge?
Or USB chargeable that lets you keep using the light while you are charging, and gives you light 24 hours around the clock?

If the second, then what you want is a regular headlamp, two or three rechargeable batteries, and a USB battery charger. The chargers are cheap, and it's no harder to plug a USB cable into a charger than to plug it into the light. The difference is that if you plug it into the light, then you cannot use that light while it is recharging. And when that battery goes bad, you may have to throw out the whole light.

For arms-length work, you cannot beat the Zebralight mules, i.e. the H502 and H602 models, using either AA-format or 18650 batteries. For your price, it may be too expensive to get the 600-series. But the AA-series is amazingly bright on Eneloops or on any rechargeable AA. And you can always use alkaline if needed.