Financing for holiday homes is treated as a commercial mortgage transaction. If the property has not already got a record as a successful holiday let, in the current climate, it is unlikely that you will find a lender that will provide finance based on future income projections alone.
If however, the property has been used successfully as a holiday let, the financing you will get will depend upon the historical letting history and/or what income could be achieved if the property were to be let on a standard Assured Shorthold Tenancy agreement (which is normally lower than what can be achieved from holiday letting income). If the property is subject to letting restrictions (and you must declare this information upfront to any lender) it may be harder to secure finance. This can be a tricky area, so I recommend that you speak to a commercial broker (such as Mortgages for Business!) to advise you on the available options, if any.