There are many sources in England for giant vegetable variety seeds. As for Mr Lavery I think he is no longer in the giant vegetable seed business. But their are several good giant vegetable seed supliers in the uk.
Finding good specimen seeds is alway a problem. You need to find the growers themselves to get seeds of some giant types. I suggest you try asking questions on the site below.
What giant vegetable seed types were you looking for.

Here is a link that might be useful: bigpumpkins.com

Bernard Lavery passed away some time ago.

He is alive and well. Read Erick Shackels interview he he did with Bernard about his world record cabbage. Later.

I've heard this rumor several times that he passed away. I correspond with him; so I know that is not true.

Here ya go...

Here is a link that might be useful: Bernard Lavery

Bernard Lavery was working for an Arab prince last I heard . you can get some of his varieties from "Thompson and Morgan" also check Ken Whealeys book "seed inventory " (latest year available) , and the U.S.A. germplasm GENE BANK ,SEED BANK . Bernard Lavery's book "I can grow " will give you other help . good luck.