Not absolutely sure but I think the first sub used by England was Tim Dalton (Coventry) in 1969. (I'm fairly certain it was the first time England had used a sub in a home game; I watched it on TV and I was a Coventry fan, so I remember it well).
This link just confirms Tim's cap in 1969.
http://www.schoolsrugby.co.uk/schoolSportHistory.asp?Id=258
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No substitutes were allowed for any reason in the 1966 World Cup. Some previous finals had allowed substitutions for injury and from 1970 substitutes were allowed for tactical purposes.