You are only required to keep the old log book for 2 years since the date of the last entry.
Transfer the summary totals to your new log book and sign it.
You will not need to send either log book off to the CAA - and any good Flight Examiner should be able to give you a Form FCL 150CJAR for your licence after you pass your renewal skill test. Your licence will then be valid as soon as he/she has signed the form.
If you have an ancient style PPL (that tatty plastic thing) and want new style licence, stress to the CAA that you do NOT want a JAR-FCL PPL (which only lasts 5 years), you want your lifetime UK PPL re-issued in the new format. There may be a CAA fee if you want the licence reissued though.