Hi Briony, sorry for my slow reply,
The "official" way to check a miner's background would be via the Records Office in Gloucester, as per this thread,
http://forum.forest-of-dean.net/index.php?mode=thread&id=42376

However from this site's Register I'm pleased to find this entry, does it seem to fit (you didn't give any indication of dates etc) ?

Forest of Dean Freeminers Register
Transcript Details

Record_Number: 3818
Forename: William George
Surname: LATHAM
Calculated Year of Birth: 1888
Age: 40
Day: 2
Month: Jul
Year: 1928
Residence: Five Acres Coleford
Remarks: Certificate of Birth produced
Memorandum:
Soundex: L350

Also, from this sites Parish Registers Database, can find:

Baptism:
Record_ID: 6005
Entry_Number: 296
Year: 1887
Month: Sep
Day: 11
Parents_Surname: LATHAM
Child_Forenames: William George
Fathers_Forenames: John Francis
Mothers_Forenames: Mary
Mothers_Surname:
Residence: Lane End
Occupation: Hostler
Officiating_Minister: D. J. Banham (Curate)
Event: Baptism
Memoranda: Born Aug 2nd 1887
Notes:
Register_Reference: P82 IN 1/5
Page_Number: 37
Parish_Chapel: Christchurch
Soundex: L350

Marriage:
Record_ID: 82031
Entry_Number: 25
Year: 1920
Month: Feb
Day: 11
Grooms_Surname: LATHAM
Grooms_Forenames: William George
Grooms_Age: 32
Groom_Condition: Bachelor
Grooms_Occupation: Haulier
Grooms_Residence: Cannop
Grooms_Fathers_Surname: Latham
Grooms_Fathers_Forenames: John Francis
Grooms_Fathers_Occupation: Haulier
Brides_Surname: FARR
Brides_Forenames: Irene
Brides_Age: 23
Brides_Condition: Spinster
Brides_Occupation:
Brides_Residence: Five Acres
Brides_Fathers_Surname: Farr
Brides_Fathers_Forenames: William
Brides_Fathers_Occupation: Collier
Licence_or_Banns: Licence
Date_of_Banns:
Signature_or_Mark: Both Sign
Witness_1: William Farr
Witness_2: Henry Sydney Brown
Other_Witnesses:
Officiating_Minister: C Barnes
Event: Marriage
Memoranda:
Notes:
Register_Reference: P52 IN 1/8
Page_Number: 13
Parish_Chapel: Christchurch
Soundex_Groom: L350
Soundex_Bride: F600

Burial:
Record_ID: 248464
Entry_Number: 508
Year: 1954
Month: Apr
Day: 2
Surname: LATHAM
Forenames: William George
Residence: The Gardens Five Acres
Age_at_death: 66 years
Officiating_Minister: H.Bryden Vicar of Christchurch
Event: Burial
Cause_of_death:
Memoranda: re-open new church yard row 1
Notes:
Register_Reference: P82 IN 1/17
Page_No: 64
Parish_Chapel: Christchurch
Soundex: L350

NB: This website's PR database doesn't have any for the "Leatham" spelling, but has 48 for the "Latham" spelling.
http://www.forest-of-dean.net/index.php/parish-records-search

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Here's the family on the 1911 Census, from the free-access Ancestry site:

Five room Household at "The Stables", Near Cannop, Coleford, Glos

Name Relation to Head Birth Date Age Gender Marital Status Occupation, Birth City Birth County Birth Country
John Latham Head 1847 64 Male Married 36yrs Horse Keeper For Stone Firms. Coleford,Gloucestershire,England
Mary Latham Wife 1857 54 Female Married 36yrs. Coleford,Gloucestershire,England
Tom Latham Son 1876 35 Male Single Collier (hewer). Coleford,Gloucestershire,England
William Latham Son 1888 23 Male Single Horse Driver. Coleford,Gloucestershire,England
Frederick Latham Son 1890 21 Male Single Horse Driver. Coleford,Gloucestershire,England
Mary Latham Daughter 1892 19 Female Single Dressmaker At Home. Coleford,Gloucestershire,England
Alice Latham Daughter 1895 16 Female Single Dress Making Apprentice. Coleford,Gloucestershire,England

http://interactive.ancestry.co.uk/2353/rg14_31728_0367_03/1424798?backurl=http%3a%2f%2f...

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Do you/your dad know the Forest area ?. If not Five Acres area is easy to find, it's at Berry Hill slightly outside Coleford heading east toward Cinderford.
Christ Church as mentioned in the above PRs is detailed here, also a usefull local map
http://www.achurchnearyou.com/parish.php?p=160088/
Click "contact" tab on this page to open Map
http://www.achurchnearyou.com/christchurch-forest-of-dean/

"Five acres", Berry Hill is the home of the local Royal Forest of Dean College, their postcode is GL16 7JT.
Also see
http://en.wikipedia.org/wiki/Berry_Hill,_Gloucestershire

http://www.westdeanpc.org.uk/berry-hill-and-christchurch/

I hope this is "your" man !?

PS there's a wellknown local author called Joyce Latham who's written about the early years of her life in the 1930s/40s Forest, a relative perhaps ?. She's mentioned in this list, the rest of this website may help your dad's visit
http://www.fweb.org.uk/dean/deanhist/books.htm

Coleford, near Five Acres, has an excellent independant bookshop that carries many local history titles including Joyce's, a recommended stop for your dad I think.
http://www.forestbookshop.com/pages/Categories/075094885x.html