The highest contrast ratio of the LG 23M45 is 1000:1. That's 100% less contrast ratio than the most common dynamic contrast ratio of 20000000:1. The contrast ratio of all medium monitors that have been available for a comparable time to the 23M45 ranges from Mega Contrast to 100000000:1.
It may also be worth also looking at one of the other flatpanel monitors that have a 1000:1 dynamic contrast ratio currently available including the LG 24M45 (£115.81) which has a better Rating; or the Asus VS228D (£49.99) which is cheaper.
PC screens with a higher contrast ratio that might also be worth looking at include the ET220a (10000:1 and cheaper), or the ES240d Slim (£113.93) (10000:1 and cheaper) both from Edge10; or the HP ZR22w (£140.26) (3000:1 and higher rated).