Could I get a normal BTL mortgage on a property and use it as a holiday let or is that super naughty?!!
If you read the T&Cs that pretty much all standard BTL lenders issue, you’ll find these conditions within them
1. The minimum rental term permitted is 6 months
2. The maximum rental term permitted is 12 months
3. The only permitted rental contract is an Assured Shorthold Tenancy (AST)
Doing as you propose breaches 1 & 3.
The lender may not catch you doing this, but if/when they do, you have given them grounds to call in the mortgage. You will receive a Cease & Desist letter ordering you to revert to AST renting or face repossession if you don’t. This will be investigated to ensure you have complied.
As Clint Eastwood memorably said "so, do you feel lucky?"
You may conclude it is a safer bet to get a mortgage without the above conditions and there are a few lenders who specialise in this kind of mortgage. What you need is a good broker who knows their way around this kind of lending (get in touch if you want more information about this).
While property investment, like any other investment strategy, always involves some element of risk, it doesn’t make sense to load the scales against yourself. You might also find this blog about serviced accommodation useful.