Well, thanks to web-based service Payscale , you can easily find out. Or rather, you can find out what the typical salary and benefits package for a particular job title is in an industry sector. And it covers the UK. What's interesting is that it takes into account things like years of experience, etc. Having done a quick test it does seem to provide a pretty accurate guide.
According to this, the average technology company marketing director has a base salary of around £70K per year - the highest salaries just topping £100K per year. Other benefits such as bonus, etc can add another 20 - 30K to these figures.
Tom Foremski has more detail here - interesting that the av. Silicon Valley VP of marketing earns around $165K per annum - or around £87K - so not terribly dissimiliar to the UK.
HR Exec press release: http://payscale.com/about.asp?pg=news⊂=pr&pr=101