Your site is very, very heavy at 4+ megs. Lighten it up; see http://gtmetrix.com/reports/www.moseleycoachsales.co.uk/eyz4qxQx
Fix the code errors, such as not specifying image dimensions, not correctly scaling your images, not optimizing your images, setting browser caching and expires headers, etc.
Your site speed has very little to do with one 404 for one style sheet. Use Firebug with Firefox, or use the developer tools in Chrome or Safari or IE to see what’s loading on your site.
Your database may be oversize from revisions and your theme may be using more than the average number of queries. Use http://wordpress.org/plugins/debug-queries/ and http://wordpress.org/plugins/rvg-optimize-database/
And, every inexpensive host out there is slow. Check http://www.google.com/search?&q=123-reg+slow