Replacing the worktops wasn't an option for me. I don't have the gear or the skills to do it and getting someone in was too expensive. So I did pretty much what I said in my first post. It wasn't quick and I needed much patience but it worked our really well (and really cheap!)
So I thought I would update this thread with more detail just in case it comes up on a search for anyone wanting to do similar.
Most important was getting a large enough piece of matching laminate to effect the repairs. Edging strips were too narrow for the largest hole so I contacted the supplier (name printed on the underside of the worktop) and sent them a photo. They sent me (for nothing) an A5 sample of the matching worktop. I thanked them. A lot!
I then carefully cut two near-perfect squares of laminate from this using a steel ruler, scalpel then a stanley knife and lightly sanded the edges. These were to be the patches for the holes. I also used them as templates to cut squares around the holes in the worktop, again using a steel ruler, scalpel then a stanley knife. This took a long time - two or three hours. I found that the "waste" pieces of laminate (ie that on the work surface between the irregular holes and the squares I cut using the templates) lifted out quite easily using a scalpel, stanley knife or small chisel on the edge especially if I scored the waste sections from the hole to the cut I had already made.
Next I made plugs for the "meat" of the holes from some spare flooring grade chipboard I had. I had traced templates of the holes before I cut the laminate out and used these to cut over-sized plugs with a jigsaw. I sanded them down until they fitted snugly into the holes (took a long time) and glued them in place with Elmers wood glue, being very careful to get the top of the plugs flush with the particle board that was revealed when I took the waste laminate out.
For good measure I put a thin coat of Elmers over the whole of the exposed particle board as it's waterproof and I hoped would provide some protection from water penetration. I then left the whole lot to dry for 24h.
Next, I dry fitted the patches into the holes and removed whatever was necessary to get a good fit very , very slightly below the good work surface (and certainly not proud.) To do this I used my scalpel, medium sandpaper and a small but very sharp chisel, being very careful not to lift any more laminate. I also sanded the edges and corners of the patches to make the fit as good as possible.
When I was happy with the fit the patches were fixed over the plugged work surface using Evostick Impact contact adhesive and held in place until I was sure the bond was good.
Finally, I used colorfill (following the colorfill instructions) to fill the gaps between the patches and the good work surface. I did this in two passes, leaving 24h to dry between each.
The results? Very impressive and near invisible to the casual glance.
Time will tell if they will stay stuck and remain watertight. I'll post an update in six months time.
