Hi
From a marriage index.
Hampstead registers are not covered by the IGI (see Hugh Wallis' website for IGI coverage though it is not completely up to date for recent additions from Bishops Transcripts)
http://freepages.genealogy.rootsweb.ancestry.com/~hughwallis/IGIBatchNumbers/CountryEngland.htm#PageTitleThe Ancestry digitalisation of the parish registers held at the LMA and the Guildhall is of course still quite patchy for the period where the registers have been indexed (post 1813 for baptisms and burials, post 1754 for marriages).
For St John Hampstead (the parish church) if you check the coverage it is 1801-1810, 1828 and complete from 1837 onwards.
The usefulness of Ancestry is it clearly indicates in the drop down menu its coverage so far of each church's baptism, marriage and burial registers
In this post I gave details at the time of the sort of coverage for marriages the Ancestry project had so far achieved using as an example just the churches in the square mile of the City of London and what was still missing.
http://www.rootschat.com/forum/index.php/topic,430983.0.htmlThe IGI is an imperfect index and so is Ancestry at this point and will be for sometime to come because the project that has been taken on is really quite enormous. Other marriage indexes are also imperfect as far as the London area goes, but taken as a whole there is now a far greater chance of finding marriages. The other marriage indexes which are still important to check, other than the local family history societies indexes which are not online, are Phillimore, Boyds and Pallots.
They are all detailed in Dawn's very helpful guide at the top of the London and Middlesex boards
Requests for parish register look-ups - Important information
http://www.rootschat.com/forum/index.php/topic,404050.0.htmlRegards
Valda