Hi Sandy man,
I'm in the same position as you, having received a text about my appointment this morning for a blood test at King's.
This was ordered in early June at an outpatient appointment. From what I understand, unless your form is marked URGENT, they will not take your blood.
I don't think there is any point in attending, but I'll ring this morning to check. This situation could go on for months apparently.
Update: I phoned and they confirmed, do not attend unless your form is marked URGENT