If you move to a proper business-grade ISP then you should get a bigger bite of the pie, as it were.
Things to look out for: You only have BT Wholesale at your exchange and BTW offer their resellers 2 choices - standard and elevated services. This used to be called 50:1 and 20:1 contention, but BT measure things somewhat differently now...
Some ISPs will sell you a "Business grade" connection to mean that they give you more data, NOT move you to the elevated services. This is something to look out for. On your exchange, moving to elevated services will take your upstream from a max of 488Kb/sec to 832Kb/sec. Make sure you look out for a package that will give you the higher upstream or it's not on the elevated services!
Other things should be different too - the ISPs connection to the BTW network - hopefully it's "fatter" and also hopfeully the ISPs internal network is un-contended too - and they have better connectivity to the main peering points and so on.
So moving to a good business-grade ISP should give you more throughput, however it's unlikely to give you a higher speed as that's limited by the kit in the exchange (and distance) The trade-off is that decent ISPs usually have a well-defined data usage cap/allowance rather than some wooly fair-use policy, or acceptable use policy. They are also a bit more expensive and only you can tell if the additional cost is worthwhile. But do note that most of them only lock you in for one month at a time, so changing is relatively easy. (Remember to get a MAC)
Then it's just down to picking one that you think is good (read the reviews) and worth the additional money. I'm on a rural excange using an Entanet package (I'm an entanet reseller), and in-general I appear to get a much better level of service than my neighbours who're all on the cheap and cheerful packages from Sky, BT, TalkTalk, UW and so on... (At least that's going from the comments I get when they visit me and use my broadband)
I think the main niche ISPs have been mentioned in the thread - The usual suspects - Goscombe, An Entanet reseller on their busines packages, Zen, ADSL24, Xilo, etc. The "ultimate" is AAISP, but that comes a a price, however their service is (AIUI) 2nd to none.
As for your telephony - you need a decent router than can do QoS - however I'm not at all sure if they can recognise Skype, but I have had good results with the Billion 7800N router and SIP VoIP. I used to use Drayteks have have found them to be very hit and miss as of late with NAT issues on long-term sessions requiting a reboot.