Interest relief for rental property

Can a deduction be taken for interest on own home against rental property income in any of the following situations:

1.  own home has no mortgage I then buy a rental property but raise the mortgage on my own house so to avoid higher buy to let interest rates. As the only reason for getting the mortgage is because of the new house purchase I am of the opinion the I can claim full relief for the interest. Do you agree?

2.own house has a mortgage for half the value. I raise a mortgage to increase this to the full market value of my house snd use the money to buy a rental property, the rest of the purchase price beig via a buy to let mortgage on the rental property.  Would you agree I could pro-rate the mortgage interest on my own mortgage to claim an element (the increased element) against the rental property?

Any opinions are appreciated.

Thanks