The reason this happens is that GP practices are trying to ration out their appointments to ensure there is reasonable access. However, the implementation that most of them choose to use is pretty crappy because it makes patients feel uncomfortable and isn't particularly effective.
Receptionists aren't the right people to do triage in this way. Triage should be done by the most senior clinician available it's faster, safer and more likely to be accepted by patients. Receptionists like those at Sidge's practice terrify me that "basic medical training" is a perfect example of a little knowledge being a dangerous thing, and encourages receptionists to tell patients that their requests are "wrong" in some way. The algorithms are completely inadequate to the task at hand. Algorithms work well for blue-light services because the range of life-threatening emergencies is much more limited than the full range of medical conditions, and because massive international effort has gone into developing them for this purpose. The same is not true of general practice.
That's why there are some practices (like Stour, in Devon) that have GPs answering the phones. A third of the time, the GP tells the patient how to care for themselves without coming in. Another third of the time, the GP says "come in and see the nurse". And the final third, the GP gets the patient to come in to see a doctor.
But you only really need to do triage at all if you've not got the right number of appointments at the right time in the first place. Lots of places provide good access without any triage at all.
Incidentally, Sidge, this isn't true:
"Well receptionists are bound by the same confidentiality agreement that clinical staff are."
Receptionists sign a confidentiality agreement with a practice. But nurses and GPs are bound by NMC and GMC codes of conduct, and risk being unable to practise their profession if they breach the rules. The bar is much higher. Patients by and large don't want to disclose private medical information to non-clinical staff, and that is perfectly reasonable.