@Matthew1659 Depending on what action do you take to keep below £85K the answer will be different.
Some guesses and ideas below - Happy to work it through again with better inputs
Lets assume you currently shut down for 20% of the year (ie 10 weeks) to keep below the limit and that 20% of your costs are VATable at the full rate
New scenario - Open all the time
Increase in revenue = 15% ( I am assuming you earn less when you have been shut down (Winter) = 12750
New revenue =97750
But if we assume a guest will not pay more than they pay today you will have to reduce this amount by the VAT you will pay (ie reduce by 20% - not quite the right amount but close)
So revenue for compete year is 97750/1.2 = 81460
Increase in costs as you are open more (assume 30% of costs are variable) =.2*35000*.3=2100
Decrease in costs = 20% of 20% of 37100 = £1484 as you can claim back VAT on some costs
So new profit is 81460-37100+1484=45844 which is less than your current profit.
Now if you are shutting down for 50% of the year the sums will be very different.
Finally if you own the place with a partner could you have two listings and each have an 85K allowance? No idea if this is legal and you would need to talk to an accountant!