One of the must haves for UK juvenile SF collectors is the Kemlo series by E. C. Eliott (one of the many pseudonyms of Reginald Alec Martin). Most of the books are available even with undamaged dustwrappers if one can afford the usually three figure prices. All the books were published in hardback by Thomas Nelson with only four appearing in paperback editions.
Kemlo and the Crazy Planet (1954)
Kemlo and the Martian Ghosts (1954) – published in paperback by Nelson Juniors in 1959
Kemlo and the Sky Horse (1954)
Kemlo and the Zones of Silence (1954) - published in paperback by Nelson Juniors in 1960
Kemlo and the Craters of the Moon (1955)
Kemlo and the Space Lanes (1955) - published in paperback by Nelson Juniors in 1959 and again by Hamlyn (Merlin Books) in 1968
Kemlo and the Star Men (1955) – published in paperback by Hamlyn (Merlin Books) in 1968
Kemlo and the End of Time (1956)
Kemlo and the Gravity Rays (1956)
Kemlo and the Purple Dawn (1957)
Kemlo and the Zombie Men (1958)
Kemlo and the Space Men (1959)
Kemlo and the Satellite Builders (1960)
Kemlo and the Space Invaders (1961)
Kemlo and the Masters of Space (1963)
All the information comes from www.reginaldalecmartin.co.uk which site also provides details of non-UK editions.