Ah, sorry I was under the impression you had certificates for the big stuff.The electrician has just mailed me and said to say 'yes' we had works done but they were all non notifiable works under section 'P'
Yes, a consumer unit (trip switch system) change is notifiable. He should have issued a certificate at least, which will be an Electrical Installation Certificate.
You should also have received Minor Electrical Installation Works Certificates for the minor work, but this work won't be as obvious as a new consumer unit so I wouldn't be worried about it.