It depends. If your employer or your own Limited Company provides you with a van, HMRC usually assume it will also be used for personal journeys.
They will tax you personally on £3,600 (2022/23) for use of the van as a ‘benefit in kind’ (and a form P11D will need submitting to HMRC), and on £688 (2022/23) for fuel if this was also provided by the employer. These amounts are generally much less than you pay having a company cars.
If the personal use is minimal, say slight detours to school or a couple of trips a year to the local tip, then the benefit won’t need putting on a P11D and tax will not be due. But, if you use it for shopping, holidays etc., there will be a taxable benefit in kind and a P11D will be due and tax will be payable.
I recommend that you keep a log of all your journeys and reconcile them to mileage meter readings, in case HMRC ever question your personal use of the van.