Collect relevant earlier and current employment records, departure and rehire dates, and evidence of the roles actually performed. Identify changes in legal entities or job responsibilities.
Preserve the break in the timeline
Do not merge two contracts into one apparently continuous appointment. Explain the gap accurately and let the applicable employment rules determine which evidence is relevant. Rank the records before requesting them.
A payroll register, tax slips or the equivalent statutory earnings record generally establishes when someone was employed and by whom, and it is produced for reasons unrelated to this application, which is exactly why it carries weight. Employment agreements establish terms and title. Reference letters establish neither and should be treated as commentary.
Where two contracts exist because the person left and returned, keep them as two documents with two sets of dates; merging them into one narrative of unbroken service is the error most often undone later, and undoing it is harder than presenting the gap honestly at the outset. Hypothetical example: a medical laboratory technologist rejoins a group whose foreign entity was renamed during the absence, and only the corporate filings show that the employer before and after is the same qualifying organization. Request archive material early, since employers rarely retain payroll detail in a form that can be produced within a week.