The total number of homes sold to first time buyers is not collected. Although data on all house sales in England and Wales are collected by the Land Registry there is no information collected on buyers.
Information on mortgages to first time buyers and former owner occupiers for house purchases in the UK is collected by the Council of Mortgage Lenders (CML). This includes the total number of loans to first time buyers and the percentage of loans to first time buyers. This information is published on their website at:
http://www.cml.org.uk/cml/filegrab/2ML2.xls?ref=4624.
Information on mortgage sales at county or constituency level is not available.