Nowadays a lot of people search for jobs online. If you are doing this, you will need to make sure you can produce copies of the adverts and your application for the tribunal to show that you have made reasonable efforts to get another job (and thereby mitigate your loss).
Online adverts and applications can complicate this process, because it can seem as if you have a record when you don’t. For example, an email with a link to the advert on a website may seem to be a good record. But, six months later, when you’re preparing a mitigation bundle you may well find that the website has changed and there is no trace of the job or its details.
To be safe, make sure you have a full record of the advert yourself. The easiest and simplest way of doing this is to print it out there and then. Or to save it as a pdf.