When to upgrade the fusebox?

[Spoon]

right but this would have to go outside the cabinet because there is no space left right of the unit

So would a longer consumer unit not then clash with the side of the cabinet?
Your pic doesn't show the whole cabinet.

 

[MalcolmS]

This is the whole cabinet. The electrician has said that a bigger fuse box can fit in.
I am just not sure if I want to upgrade the consumer unit at this moment of time which will be £600-700.
I mean installing another smaller box outside the cabinet will also cost but perhaps it makes more sense at this time. In any case this seems to be a blocked to get the electric shower installed.
I reckon in couple of years the requirements will change anyway as I want to electrify the backyard. Electric sockets in the shed, garden lights but there is no shed as of yet.
But then I will have to make the cabinet bigger anyway and perhaps even get more space for PV equipment.

 

[brianmoooore]

The FCU above your CU, and the RCD to the left will probably be gone when a new CU is fitted, so there's more space available than just the footprint of it now.
A matter of measuring the space and checking manufacturer's specifications to see if any will fit.

 

[MJPD29]

This is the whole cabinet. The electrician has said that a bigger fuse box can fit in.
I am just not sure if I want to upgrade the consumer unit at this moment of time which will be £600-700.
I mean installing another smaller box outside the cabinet will also cost but perhaps it makes more sense at this time. In any case this seems to be a blocked to get the electric shower installed.
I reckon in couple of years the requirements will change anyway as I want to electrify the backyard. Electric sockets in the shed, garden lights but there is no shed as of yet.
But then I will have to make the cabinet bigger anyway and perhaps even get more space for PV equipment.

They will change in a couple of years, and will continue to change every couple of years continuously thereafter. Regulations and rules will always be updated.