Hi Martyn,
Windermere – the rules for motors, registration numbers etc. seem to change almost annually, and I haven’t visited for about 18 months, however, last time we were there we launched and kept the boat on some National Trust land at Harrow Slack, immediately north of the ferry terminal on the west side, about half-way down the lake. The charges are much less than anywhere else that we enquired about. A warden may come and collect your fee and issue a ticket, otherwise I believe there is an honesty box and/or an arrangement to pay at the nearby NT property. The Trust’s view as I understand it is that sailing is in keeping with their ethos (sustainability etc) and visually and acoustically fairly unobtrusive, hence the sail-friendly attitude to date. Let’s hope it stays that way.
Poole Harbour – Redcliffe Farm is fine as long as you are prepared for the jaunt through the reed beds down the Wareham Channel each time you want to sail on the broader expanse of water in Poole Harbour itself. With a motor this is no problem, but it inevitably takes up some time. Nice short walk into Wareham and good access by car to Purbeck etc.
Good luck.