I have worked for Tesco before. I had a Saturday Job with them years ago as well as managed their tech department when i did some work in retail between university and getting a proper job.
They are ruthless with till shorts. Temporary workers are usually given one chance if there is a short over £5. Permanent workers have two warnings, the first lands them in a meeting with their line manager. Second one with the store manager and the last usually is a dismissal.
They don't need proof (other than what the till or checkout manager records) as each till is till checked between employee changes with the old system. If they have the new system then each till draw section is weighed during each transaction. Mistakes/thefts can be found as the time, employee number and amount of money in each till section is recorded and calculated by weight. Tesco does not differentiate between theft and loss.
Give the money back, a mistake can be acceptable if the money is returned but all discovered shorts are treated as theft until resolved.
Stock shorts always happen and a medium size extra store in Surrey usually has about £400-600k of shrink over a 6 month period (this doesnt include any stock noticed to have disappeared by the internal stock checks which happen daily).
Smaller stores have the freedom to be far more lax with till shorts for some reason another as they are usually kitted out with the leftover old kit which doesnt record everything that passes through the till and till managers dont have time to always perform a till check.
