Charging a lower rent for the right tenant

 Hi
 
 I have just purchased a buy to let and would like to set the monthly rent lower than what the letting agent has recommended. The income from what i want to charge will still cover the interest easily plus all the other expenses associated with being a landlord. It is also my intention to make use of the annual 10% allowed for paying of more capital on the property.  The repayment on the interest only mortgage is not high, probably equivalent to going out for a nice meal. My plan is to completely refurbish the property as it is in a bad way and sell it on in 3-5 years time. I have a tenant in mind who is more than happy to live there while the work is ongoing and this is why I am prepared to under charge the going rate. Will my mortgage lender need to know I am not charging the full recommended monthly rent and will this become a nightmare for my tax returns.I am all new to this and do you think i am over thinking things.

Thank you

 Thank you Hippogriff