Job description

Hi, we're buying an old home in which the electrics are around 30 years old, but with a new consumer unit. Wires running out of the consumer unit are grey pvcu. The question is do we need a rewire?

Are there any rules on when or why we'd need to rewire? Would the current set up be fine with extra plug sockets added? I'm not sure if there are rules on this by age or whether each house would need to be checked over individually. If an individual check is needed we'd be keen to get someone to check over the electrics in the property and let us know if any work is required and costs.