No whilst you are doing the ONP if you are supported by a hospital you will earn a band 3 or 4
I suspect that will probably be the case, as it;s quite common for newly qualified Nurses to be paid as band 3 / (in the past whitley B) until they get their PIN through - a lot of trusts used to back pay at band 5 (Whitley D in the past) to the date of appointment, whether this continues we'll have to see.
In London they pay a band 4 for the duration of ONP, until NMC issues a pin number.
But a word of caution, they are not exactly pro-active in chasing the universities for the paperwork to send to the NMC. I have co-workers who have been over 6 months since completing ONP but still waiting for a pin, and still on band 4. I've heard of some nurses waiting up to 14 months, still on Band 4, even though they are experiences RNs and have completed ONP.
SO don't take on any financial commitments such as a mortgage assuming that you will move to Band 5 as soon as you complete the ONP.