Get an Airspace map and have a look at the bases of controlled airspace. We can't descend below 5000ft until you are about 14/15 miles from touchdown and then we can only drop you to 3000ft.
Check out
http://www.ais.org.uk/aes/pubs/aip/p...s/32GW0401.PDF
If you look at the chart you are transferred to the Luton Controller in the top right hand corner of airspace. It's then usually an immediate left turn on to a base leg (for 26) followed after a few miles a descent and speed reduction. If you need a descent earlies it will probably involve giving you about an extra 8/10 miles to get you in to the airspace were we can descend you, unless of course you don't mind leaving CAS. But be aware there are usually many aircraft under the CTA at 2400ft outside CAS