how much does a chinese visa cost for uk citizens going on holiday there are 2 adults and 2 children

For UK citizens, visa fee is GBP 30 for a single entry under regular processing. But if you are required to apply for China visa through CVASC (in London and Manchester), you need to pay their extra service fee of GBP 36. So, check their consular districts first if you need to go to Chinese consulate or CVASC.