That sound like Oxford's own rule. I enrolled on a DL course then due to circumstances, didn't actually start studying until nearly two years later. I explained the situation to the school and they agreed to honour the course fee I had paid prior with no extra to pay. I then started the studying, brush-up courses etc and finished a further year later.
I am not aware of any JAA rule which states you must complete the groundschool in I8 months so if this IS the case, please quote the relevant section from JAR-FCL.
Rishy, if it may take some time to build your hours to 50, get some second hand manuals and start now if you want. You will, of course, get another set of manuals when you enrol on a course. There was a website (but I've lost the link) that published the Jeppeson/Atlantic Flight Training manuals in .pdf format for online, free viewing.
Cheers
Whirls
Edit - look what I found
Index of /materialy/testy
OK, the site is Polish and this is the root directory but you can download some manuals and the Volare Italian Question Bank.