ISPs: How much for how much?

I switched ISPs a couple of weeks ago. I was using Zen but now I’ve migrated to Be. The whole process was surpisingly simple and I lost Internet access for all of about 15 minutes.
I would have stayed with Zen since they were reliable and competent, which really carries weight in the world of Internet access. But they were charging me £29.99 a month for uncapped 1Mbps Internet access. I could have gone to their capped 4Mbps service, but the cheaper option had a limit of about 2K or something while the reasonable option (50GB per month) is about £35. So I decided that while they were good, they weren’t that good and migrated to Be.
So far, Be have been pretty good. I had an outage on the first day, but since then they’ve been fine. But Be’s selling point is they’re an ADSL2+ service – they advertise with the tag of “£24 per month for 24Mbps”. It’s uncapped (hooray!), but there is a “fair use” policy (aka “If we want to cut you off for any reason, we will and there’s nothing you can do about it.”) There’s also a tiny bit of small print – you won’t necessarily get 24Mbps since the exact speed depends on your distance from your telephone exchange.
I’ve checked around a bit and no one I know who uses Be has ever got more than 5Mbps or so. I’m getting 4.7Mbps now, which is a hell of a lot less than 24Mbps, but much better than the 1Mbps I was getting with Zen.
Nevertheless, I have a question: If it’s £24 per month for 24Mbps, since I’m getting 4.7Mbps, can I pay £4.70 per month instead?