The power rating for speakers is the maximum power they can handle before damage to them is likely to occur. The power rating for amplifiers is the maximum power that it can deliver. However, you need to be careful when matching speaker/amplifier power ratings since different manufacturers rate their power differently. This is due to the fact that power can be expressed in terms of RMS, Peak or Peak-to-Peak. It is important because each is calculated differently, the following are conversion formulas:
RMS = Peak X 0.707 or Peak-to-Peak X 0.3535
Peak = RMS X 1.414 or Peak-to-Peak X 0.5
Peak-to-Peak = RMS X 2.828 or Peak X 2.0
Make sure that when matching up your ratings that they are on equal terms, if the speakers are rated in RMS and the Amplifier is rated in Peak, then convert the speaker RMS rating to Peak or the amplifiers Peak rating to RMS, then you can see how they fit on an equivalent scale.
Another thing to keep in mind is whether the power rating is specified as "MAX" or "Continuous". "MAX" means that it can only provide/allow that level for a short period of time, while "Continuous" means just that, the the amp can deliver of the speaker can consume that much power continuously.
The speakers will only draw as much power as the source (amplifier) provides, and the amplifier delivers lower power at lower volume levels and maximum power when it is cranked all the way up.
If your speakers are rated for 250W per channel/speaker, then make sure the amplifier you select only provides a maximum of 250W per channel/speaker to avoid potential damage. I recommend getting a slightly lower amplifier rating vs the speakers it will be driving just to play it safe.
Another consideration is if you have a bass/treble control or an equalizer that allows you to adjust various frequency delivery. The power ratings of the amplifier are based in "normal" mid-level settings/ranges. If you change the bass/treble or equalizer settings/levels, you can throw the ratings out the window.
Finally, a good set of speakers will usually allow a cheap amplifier sound good, and a better amplifier to sound great. However, even the best amplifier will sound like crap if it is attached to a cheap set of speakers. Just something to keep in mind.
Hope this helps, and I'm in the USA, so can't be of much assistance helping on specific suggestions since I'm assuming you are in the UK. Cheers!