There were 19 battalions of Home Guard units in the Gloucestershire area in the Second World War.
1st Bn Cheltenham.
2nd Bn Campden.
3nd Bn Cirencester.
4th Bn Forest of Dean & Lydney.
5th Bn Gloucester.
6th Bn South Gloucester & Chipping Sodbury.
7th Bn Stroud.
8th Bn Dursley.
9th Bn City of Bristol.
10th Bn City of Bristol.
11th Bn City of Bristol.
12th Bn City of Bristol.
13th Bn City of Bristol.
14th Bn City of Bristol.
15th Bn 31st (Gen Post Office (GPO) Bristol.
16th Bn City of Bristol.
17th Bn Wye Valley & Coleford.
18th Bn City of Bristol.
19th Bn Churchdown.
I'm not sure who holds the service records for the home guard, however you could try the veterans agency
http://www.veterans-uk.info/service_records/service_records.htmlHis service record if you do find it will tell you which units he served with and when.
If you are going to look on Ancestry make sure you put his full name when you are looking for him, I would try looking at 1911 census first.
Best of luck with your research