Helen Ainslie (hainslie @t sunderland94.fsnet.co.uk) of Sunderland writes My grandfather Leonard Horace Curl was born at 38 Cravells Road, Harpenden, on 13.04.1926. He was a foreman/warehouseman and lived at 82 Cowper Road Harpenden. (I have found the roads on multimap.)

An Edward Curl is listed at 82 Cowper Road in the 1949 Kelly's directory for the St Albans district. There were other people called Curl listed - including 2 in Cravells Road (Mrs C. at 32 & Mrs W. at 136) and another one in Cowper Road (Wm. Herbt. at 70).

Leonard then married Patricia Willis on 21.01.1950,  in the parish church of Harpenden, Herts, but I see from your website however that the Harpenden church was known as St Nicholas. Is there only one church?

The 1949 directory lists St Nicholas as the parish church, with All Saints, Cold Harbour Lane, and St Mary's, Luton Road, Kinsbourne Green served by the clergy of the parish church. There was also St John the Baptist in St John's Road. There was also a Congregational Church, 3 Methodist Churches and a Chapel and the Roman Catholic Church - together with a Friends Meeting House, the Salvation Army Barracks, etc.

 (I have searched the Catherine House index at my local LDS library but there are at least 12 Patricia Willis' available for Hertfordshire, so I am stuck)

I assume your comment about the GRO indexes (which were at one time held in St Catherines House) relate to a search for Patricia Willis's birth as there should be no difficulty in finding the common marriage index entry for Leonard Curl and Patricia. Are you sure she was born in Hertfordshire? It is not clear whether you know her date of birth.

Patricia lived at Barnville Cottage Harpenden (multimap can't find it) before they were married, her father was Lieutenant Colonel Robert James Charles Edward Cecil Willis but was retired at the time of her wedding.

There is a Bamville (or Bamwell) Wood and Bamville Farm to the south of Harpenden, on the east side of the road between Harpenden and St Albans.

Leonard and Patricia had 4 children and lived at 12 Douglas Road Harpenden in 1971 (multimap found it). [I have deleted the names of the children who may still be living in line with the policy on this site.]
 
My great grandfather was Edward Curl a gardener who married Louisa Elizabeth George.

Presumably the Edward Curl of 82 Cowper Road in 1949.

I have found most of my information through family interview and searching for B & M certificates from the Catherine House records, and I am in the process of trying to trace the great grandparents B & M details. I have searched your website for more information on Harpenden and printed off some details etc. Searched LDS family search.

You have not yet looked at census returns. If you visit the online 1901 census site you should be able to find a 17 year old Edward Curl living in Harpenden with his parents and several siblings. You may also be able to find Louisa George - perhaps with her family. With the information from this source you should be able to look more confidently for the birth and marriage certificates of the preceding generation - and hopefully locate them on the 1881 census (online at familysearch).