Quote from the UK Intellectual Property Office:
"Slogans are registrable as trade marks provided that they have the capacity to individualise the goods or services of one undertaking because they are not comprised of signs or indications which directly describe the goods or services or their essential characteristics, and are not devoid of distinctive character for any other reason".
Source (which includes examples of what can and can't be registered as trade marks):
http://www.ipo.gov.uk/tm/t-decisionmaking/t-la w/t-law-pan/t-law-pan-pan106.htm
For general information about 'intellectual property', including where copyright or trade marks can apply, start here:
http://www.ipo.gov.uk/whatis.htm
Chris