Seems to be some confusion here.
Wall connector or UMC + commando socket will give exactly the same charging rate and need exactly the same supply (*see below).
If your supply is single phase (90+% of UK homes), you will get 7.3kW. Whether or not you need a 100A fuse depends how much other load you have in the house (and does not depend on WC vs UMC).
If your supply is three-phase (v.large house, or originally built with night storage heating), then you will get 11kW. It's unlikely you need a fuse upgrade in this case. The commando socket would be a red one.
The wiring, earthing, RCD requirements etc. are all exactly the same whether you use commando socket or Wall Connector (though some electricians unfamiliar with EVs may not realise this).
Wall connector is suitable for use outdoors, not just in a garage (indeed slightly more suitable than the UMC in that case).
Wall connector is only more expensive if you consider that you "already have a UMC for free" - presumably the one that comes with the car, and so you need to unplug it and roll it up to take with you, and have no backup if it fails. If you were thinking of having a 2nd UMC to leave permanently plugged in (so you can have the original in the boot in case of need, and as a backup), then the WC is cheaper.
(*)There are two special cases where the WC does give you different charging rates:
- If you need a 100A fuse upgrade and can't get it (or you already have a 100A fuse and it's not enough), then the WC gives you the flexibility to select slower charging rates (such as 16A, 20A, 25A). The UMC doesn't support this, other than illegally installing a socket beyond what the supply can support and then manually turning down the power level in the car.
- If you have three-phase power in your house AND you paid the extortionate extra price for 'faster charging' (or, on older Model S, 2nd charger), then the WC will give you faster charging - 16.5kW (facelift car), or 22kW (older car).
The bottom line is that the WC is the best solution for a permanently installed chargepoint. The commando socket only saves you money if you make compromises on some combination of convenience or reliability.
The other option not mentioned above is a non-Tesla chargepoint on the OLEV scheme. This lacks the button on the end of the cable to open the chargepoint door, but is otherwise satisfactory and (at present) cheaper than having the WC installed.
