Thanks for your reply and for your kind offer of some teak. I have actually already bought a piece of teak on eBay which hopefully will be suitable. It is rather darker that the existing deck but I think it will be OK when cut, sanded and eventually weathered.
Thanks also for the heads up re your re-caulking article. I have gone for Sikaflex 290 DC Pro. It is described as ‘UV, weatherproof and sandable deck caulking sealant’ so hopefully it will be OK also. I have already bought a re-caulking tool (the Teakdecking Systems one is available from Boat Paints at a reasonable price) but I still have to buy a suitable sanding tool for the grooves.