Thanks for all the replies, I will look into the hire boat companies as suggested.
I have hired before for a 2 week period at a cost of around GBP3,000 so can imagine that hiring for say 6 weeks would cost around GBP7,500.
With Regards to typical boat share syndicates I did research this and found as Howard pointed out that they are not suitable for me.
However, my calculation of maintaining a privately owned boat is around GBP6,000 per year so my preference would be to split ownership of a boat between 2 or 3 persons and have annual use of say 2/3 months per year and split the maintenance and purchase cost. I have seen no syndicates set up like this, might any exist?