Hiring painter to paint external house

[Bosswhite]

Sounds like you are going to need a specialist firm not your average exterior painter /decorator,
Have you accepted the quote from the decorator yet, I suggest you have a word with him regarding the changes in the situation of the walls as Masonry Paint will not suffice.

Is the property listed, if so enquire with local Council Building Control, or English Heritage , there could be stipulations on colours and materials.

http://www.cornishlime.co.uk/articles/DecoratingOldBuildings.php