I need a lightweight tabletop/worksurface can anyone think of anything?

[KatyMac]

I wondered about a hollow door but I need 1.5m by 900 and that's quite wide

Ikea desk tops aren't generally that wide

Don't really know what to Google for - it to make a fold down sewing table and it needs to be sturdy enough to iron on

Plywood. Get them to cut it to size in b&q for free. Sand it then seal it with paint or varnish or white wash.
Comes in various thicknesses.
Could use ikea trestle table legs with it.

Really? Will that be 'not flexible' I alway think of it being quite bendy

It will be hinged on one side to fold up against the wall with legs that fold down

Cork or the bottom to make a noticeboard (well maybe not actual cork as it isn't sustainable) and padding/ cloth on the top for cutting/ironing on

Have a look at Marine Plywood - you can get thicknesses that are rigid, or would be over those dimensions. Also it is likely to be more water/heat resistant for the ironing.

P.S. Why do you think cork is not sustainable? It is harvested without damaging the tree, and since the invention of screw top wine bottles the cork producers livelyhood has been decimated.

I honestly thought cork was: my dad told me that in the early 90s and I never questioned it - sorry

Marine ply is a good call though

In the end I was given Ply (not marine ply)

So I am buying silvery backed stuff then covering it with a double layer of blanket and a cotton sheet!