In 1920 there were 957,782 live births, the record for the UK. The next boom was 1947, with over 850,000 and the next after that was in 1965 with a similar figure (had only a graph to give those last two so can't give exact numbers). The birth rate in the period post war to early 1950s was running at 16 per 1,000.
1920 and 1965 were marked peaks; the figures for years either side were much lower