Wow, ScorpioJo, you write as if you know about these things. What I know is that for a peal of bells each bell must be rung one after another and every combination of ringing order must be completed. So for three bells A,B and C there could be ABC, ACB, BAC, BCA, CAB and CBA which is six different combinations. Easy for 3 bells.
But St Peter Mancroft church has 7 bells. To ring a full peal with 7 bells there are 5040 combinations.
There is an easy way to calculate the number of combinations and a special symbol to show the operation. For 7 bells the calculation is 7! where the operation ! takes the number and then multiplies it by each of the numbers below it. So 7! = 7 x 6 x 5 x 4 x 3 x 2 = 5040. With only 3 bells the number of combinations is 3! = 3 x 2 = 6 which is what is shown with ABC. With more than 10 bells a full peal becomes an impossible feat as the number of combinations would take years to ring out.
The crossword must have been devised whilst the curate of St Peter Mancroft was eating his egg for breakfast. I found the challenge good and the need to research made it very interesting.