Licence & Class Rating
Whopity of course has given you correct info but I will expand.
You licence was issued for 5 years. The expiry date is hown within the licence. The re-issue date is shown in section 1X, Validity of the licence. Your JAA medical must be valid for re-issue. If you are not past the date then do nothing for the moment. If you are past the date, you simply send the completed form together with the current fee and the valid medical certificate to the CAA (address on the form).
Included with your licence is a seperate page entitled Cerificate of Validation or similar. Within that page the expiry date of your SEP (Land) is dated. This will have nothing to do with your licence as such.
You will need to do a Revalidation Skill Test for this. It is not the full skill test that you did for you initial licence. Upper Air work and circuits form the core. Any navigation will be done at the discretion of the examiner. If it is not 5 years since your SEPL expiry date the Examiner may date and sign the Rating page. If more than 5 years the Revalidation Page must be signed by the CAA themselves. In addition a form for this bit will need to be completed both by you and the examiner. The form is SRG/1119 and is also sent to the CAA at the same address, to record your renewal of the class rating.
From what you have described you will almost certainly need revision training and I suspect more than one hour.