Surtax, as the name implies, was a further tax after Income Tax had been paid and was usually accounted for in the tax year following that in which the income was earned (and Income Tax paid following the introduction of PAYE during the 1940s).
The average earned income in 1960 was around £750 p.a., well below half of the £2000 threshold for Surtax. Indeed, Surtax was applicable to around only 5% of the working population at that time.
Taxable earnings were calculated after a dizzying array of allowances and reliefs had been deducted from the income. Circumstances which reduced taxable earnings included marriage status, children (separately under 11, not over 15, and over 16), housekeeper or dependent relative.
See if you can unscramble the figures given in this 1961 extract from Hansard...
http://hansard.millba...41P0_19610607_HOC_498
...else try this from the HMRC archive...
http://www.hmrc.gov.u...eliefs_1948to1973.pdf