Consumer unit MCB appears faulty - can I swap for spare on unit

We have had one MCB on our consumer unit that has seemed a bit sensitive, but we've been careful about what we plug in - it's for the sockets for first floor (and oddly, kitchen).
Today those sockets have lost power, but that MCB hasn't tripped. The consumer unit is all 'on' and nothing else in the house is off. Tripping that MCB off and on makes no difference. We've unplugged pretty much everything (may have missed some, but pretty certain) and no change. Have flipped the main consumer unit switch and no change (well, everything went dark for a bit until I turned it back on ).
I'm wondering if the MCB has failed. We have spares on the consumer unit - is it feasible / sensible to try swapping one with this suspect one?
Is there anything else I could check for this MCB to see if it is faulty? The 'feel' of it is much as usual 0 spring-loaded and stays easily in the 'on' position (unlike when there has been a fault on the line in the past when it sprang back to re-trip).

Thanks for any help - freezer and central heating are on this circuit so I'm looking for something fairly quick before I start incurring emergency call-out fees from any local sparks I can find.

 

Thanks sparky, it's a GET brand. I decided to call a local firm we've used before and trust, since I figured it was worth it. He actually talked me out of an out-of-hours callout, so he should be sending someone this morning.
If it was a simple unplug/replug exercise I would be happy to try, but from looking elsewhere it looks like I'd have to open the consumer unit and that's probably a step too far for me with the incoming mains in there.
Thanks again for the response!
I'll post again with what the guy finds and does.

 

Local company responded immediately when I called, guy called when they said to expect him, friendly and professional - top service.
Problem was indeed a faulty MCB and he quickly swapped it for a spare on our consumer unit, checked the wiring into it, checked all the sockets and even helped us with the freezer - when we powered it on no light came on... turned out it was the light that had blown!
If anyone needs a good local electrical service in the Leeds/Garforth area I'd very happily recommend this firm - not sure whether it's okay to name them on the board or whether it's considered advertising, but happy to let people know if it helps.
Also, I was very pleased that they worked fully above board - no attempted 'discount for cash' (trying to avoid tax, etc.), all proper rates notified in advance, with invoicing/payment dealt with by the office, which again was reassuring and very professional.