Andrew wrote:

All the timber sections in yours go the same way which
means the bit under the window is potentially weaker. Is
there something below to support it ?

Just a batten all around the edges.

There's a join between two sections roughly where the back of the chair
hides the desk, it has 5 lengths of 15mm oak dowel in it.

Is this solid wood or does it have a strong chipboard core or some
sort of laminated construction ?

solid oak, finger jointed (breakfast bar stuff).

Really should tidy up all that wiring, it keeps growing, originally I
fitted some ikea suspended cable baskets under the desk, and it all
emerged to the top through desk grommets, then I removed them and they
never made it back yet.