There are two sensors, there are many non-OEM sensors, some costing as little as £15, find out if the garage fitted a cheap universal DIY wire up sensor or a more expensive £30 - £35 sensor.
Lucas part numbers LEB 455 and a LEB 456 (one of each required) are the sensors for the Jazz and cost around £65 - £70 for the pair, working in my car with no error lights