The Brava brake light is made up of 8 (or 9 or 10 maybe?) 3w "wedge" bulbs. The bulbs need to be replaced as a strip (or replaced with difficulty). Will this fail the MOT if one or more is out and the light is still connected?

No:

Source:
http://www.motuk.co.uk/manual_130.htm

High level stop lamps

These are lamps usually fitted in the rear window or boot spoiler of a vehicle and may consist of a number of light sources .
The lamp is one unit, so as long as at least one of the light sources illuminates when the brake pedal is pressed the lamp is deemed to be working.

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Secondly, if you don't want the risk and disconnect it, will it fail? No.

Additional stop lamps
Any additional stop lamps fitted and connected must be tested. Where extra lamps are fitted and there is doubt as to whether they are connected, the benefit of this doubt should be given to the presenter

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Hope that might help people in the future.

from what i hear from the mot center which we use at my work. if there is a 3rd brake light ,it must be working. even if one bulb is working, then its a pass. so if its there,and dont work.itll fail .by replacing even one bulb in the light strip. itll pass .

That's what I just posted?

by replacing even one bulb in the light strip. itll pass .

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True but the problem is that due to the homosexual nature of how the strip is made you can't actually replace the bulbs at all without doing your own wiring.

Here's a picture manual on how to improve this part:
PDF

lol, my Grandpa (being Polish) would love that, although we're not going down the LED route I don't think.

Don't have to be LEDs - this is just a proof that it is doable.

Yes, it's what we're doing, even hardwiring it in like that or using proper wedge bulb holders (like how it shoud have been done in the first place)

Regards for your Grandpa!