Hi, Have you checked out the parish registers of St James at Thorley, Bishops Stortford. These can be found at www.stjamesthorley.org Go to 'Links', then 'The Friends of St James', then 'Parish Registers'
There's an initial listing of Baptisms (up to 1941) and Marriages (up to 1945), which show quite a few 'Crabb's. I don't know if any of them will be yours but thought the link might be of use to you. Hope that helps