In the 1993 edition of
The Guinness Book of Names by
Leslie Dunkling, the number of births per 10,000 in England and Wales is given for a selection of years between 1950 and 1990. The figures for the two main spellings of Stephen/Steven are as follows:
1950:
Stephen 268,
Steven 32
1955:
Stephen 568,
Steven 132
1960:
Stephen 454,
Steven 202
1965:
Stephen 380,
Steven 178
1970:
Stephen 282,
Steven 195
1975:
Stephen 233,
Steven 219
1980:
Stephen 172,
Steven 160
1985:
Stephen 156,
Steven 186
1990:
Stephen 102,
Steven 96
So
Steven was a bit more common in England & Wales than
Stephen in 1985, but
Stephen was ahead in the other years of this selection.