If your company could hire someone else equally qualified, experienced and competent to do your work for £7k less, would they have any qualms firing you? What about £15k? Outsource it to India for 15% of the cost?
You are in a purely transactional relationship. You provide knowledge and hard work, and you get paid in money, prestige and satisfaction. That's it. It's your company, not your parent or sibling or friend or spouse - you 'owe' it no loyalty beyond that transactional relationship (and even personal relationships break down when they don't work out....). You wouldn't think twice about switching if someone opened up a new grocery store that was closer to your home and offered the same products for a lower price. Why is this different?
Do yourself a favour, mate. Go get the £7k + 7.5 hours of your life (almost a full work day on its own!) per week back. Good luck!