SOLUTION 678:

ACROSS

1 Messiah, 4 Camel, 7 Diet, 8 Elsinore, 10 St Lawrence, 12 Ulcers,

13 Cirrus, 15 Astrologer, 18 Sardinia, 19 Stud, 20 Stork, 21 Shannon.

DOWN 1 Midas, 2/3 Sherlock Holmes, 4 Chinchilla, 5 Moon, 6 Leeches,

9 Swordstick, 11 Brighton, 12 Ulysses, 14 Brains, 16 Radon, 17 Arno.