The IV anesthetic that causes one to taste garlic (or onions) is sodium thiopental (aka by its trade name Sodium Pentothal).
The small car "the secret partner' gets into after first meeting Beldon is a 1957 Austin Metropolitan 1500 convertible.
The £15,000 offered Beldon as his "cut" would equate to about $42,000 at the time or over $417,000 in 2022.
The airplane John is brought back from France on is a BEA Vickers Viscount 802, registration G-AOHV. Built in 1957, it changed hands numerous times over the years, with it's last known flight in 2009.
When John emerges from the dry-dock after confronting Charles, in the background is the HMS Glengyle. Built for the Glen Line as a cargo-passenger liner in 1938 for routes to the Far East, it was converted to an infantry landing ship for use in WWII. It was returned to commercial service with the Glen Line in 1948 and scrapped in Taiwan in 1971.