It's easy to get sucked into spending a lot of money. Keep an eye on every bit of the project as a slightly higher cost in some areas soon adds up.
Where we cut back:
Estimate included an allowance of £35 per sq metre for tiles (wall and floor). We quickly realised it was very easy to spend a lot more than this on tiles but avoided doing so. Look for local tile shops rather than high end kitchen/bathroom places.
Be clear what you want from your kitchen. It doesn't make sense to fit a high end kitchen in a small semi. Go somewhere that has differentiated kitchen lines and compare them in store eg Magnet and Howdens both had low, mid-point and higher point kitchens.
Think about the kitchen design and how it might add to the price. Straight runs of units are cheaper than corners. Drawers are more expensive than cupboards (but drawers can be a lot more useful!). Any kind of storage solution, internal drawers and the like, tends to add to the cost.
You can cut costs by paying for materials yourself however we found this came with disadvantages eg having to collect yourself, or be in for delivery, and it was our responsibility to check for any damage and follow up with the supplier. It actually saved money having the builder do it. Same with having the builder manage the project. We paid extra for this but he coordinated the trades and they all worked around each other which ultimately saved time (and therefore our money).
Look out for sales. It was cheaper to buy our kitchen in the sale and pay for storage for three months than pay full price.
Use as many of your existing possessions as you can. Eg dining table, appliances. You can always buy a new appliance in the future and slot it in than paying for them all brand new.