Quite early on Toots Thielemans did a version of Love remembered (Focus 3) available on his Silver collection and other compilations. Akkerman himself also later reworked the track with Claus Ogerman. There is a version of Focus 1 by The Lavender Hill Orchestra on an album called Pure relaxation. I believe there was a Danish band that covered much of the Hamburger Concerto material. The band was called Peaches and this is on their 1996 album.
PS (Thanks Kell Nordli - see his comment) In 1985 German guitar duo Les Deux Amis released Les Deux Amis Plays Focus Classics covering 15 Focus songs on classical guitar. Ansgar Krause (b 1965) and Thomas Müller (b 1958) studied under Prof Tadashi Sasaki at Academies in Cologne and Aachen. Teachers themselves, since 1971 they have played together as a duo.
They cover Love remembered- Sylvia- Focus III (inc P's March)- No hang ups- Anonymus (inc Answer, Orfeus, Euridice, House of the king, Tommy)- Soft vanilla- Le Clochard (Bread)- Focus IV (inc Janis)- La Cathedrale de Strasbourg (inc Focus I)- Focus II- Elspeth of Nottingham- Bennie Helder- Brother- Happy nightmare (variations).
A demo CD A little bit of an album from UK band The Trafns (2006) also include covers of Tommy and Le Clochard.
Orion from Focus con Proby was covered by drummer Steve Smith on Vital Information (1984). Smith played drums on Focus con Proby. The song is written by Eef Albers, who also plays guitar on both versions.
In 2018 a band called Texel produced an album ion the Focus style called Zeeming into Focus.