In that position we have a black box with a stonking great plug in fuse that's solder tagged to prevent tampering. Pulling that fuse would disconnect the meter, consumer unit (and rest of the house wiring) from the electricity supply from the poles in the road. I suspect you have the YEB equivalent, with the fuse additionally protected from tampering by a cover. Very early in our renovations our fuse was removed by the sparky for some job he needed to do, and at our first meter reading the removed solder tag was replaced without protest by the meter reader.
It's reasonable to consider it the electrical equivalent of the stop cock in the road for a domestic water supply.
It's difficult to get a scale of the thing and - of course - we don't know the rating of the cutout but those tails (the wires coming out of the top) look a little thin to me?
Wha, sorry? Oh, yes, that's the service head, the joint between the incoming cable owned by the electricity distributor and the meter tails. Every property has one. Onto the bottom of it is your main earth (green and yellow wire), which means you have a TN-S incomer (earth and neutral separate) rather than a TNC-S (earth and neutral separate in the property but combined within the incomer), this wire is very important, do not remove it.
I assume your main fuse (mentioned by Stevers) is separate.
Basically you can't do anything with this thing, the service head. It's owned by the electricity distributor, as are the cables up to the meter. Even if the cables out of the top of it do look thin, it's not down to you or your electrician to change them. Incomers often are thin, way thinner than the legal requirements for the cables after the meter, which you do own, but that's just how it is.
I have occasionally moved a service head a bit - both in my house or someone else's - but only a short distance and without opening it up and (obviously) without shutting it off.
And as for removing the security tag on the main fuse or meter, it's one of those things that everyone turned a blind eye to. The rules say you have to get the electricity company out to pull the main fuse and put it back in again, but nobody did that. I haven't worked as an electrician since 2016, so it may have changed, but every sparkie I ever knew pulled the main fuse themselves. I used to at least twist a bit of wire back on afterwards. Most didn't even do that. You can now buy the security tags on eBay, which even if they're not officially recognised, are better than nothing.