As far as the Gas and Electric are concerned, the original certificates are valid for 3 years.
After that the systems require recertification each year, so any van over 3 years old should come with new Gas Safety Certificate and Electrical Safety Certificate(Periodic Inspection Report)
It is a requirement of relevant utility regulations that these checks are done, but when , in particular, PIR's were first spoken about it caused a whole lot of anti regulation postings by caravan owners as it was seen as a money making ploy by the service centres.
However, it will become a mandatory requirement in the near future.
With particular emphasis on Gas, I have today had to isolate and label a cooker as Dangerous due to lack of regular maintainence and it producing lethal levels of CO.