Thank you for your reply and it looks like the bastardy records are only for 19th century
Not so. Any details of court affiliation orders that survive for Marylebone for 1929-1930 will be at London Metropolitan Archives, recorded (along with all the other kinds of cases heard at the petty sessions) in the court registers in series
PS/MAR/A.
Link to the online catalogue here ...
http://search.lma.gov.uk/LMA_DOC/PS_MAR.PDFThe records themselves are not online, so if you want them searched you will need to have research done at LMA, either by their own research service or by an independent researcher. There are at least a dozen volumes to look through.
For 1929-1930 the court records are accessible -- they are not closed under any 100-year rule.
You might be lucky but, realistically, relatively few affiliation orders were taken out when compared with the number of illegitimate births.