You've confused me a bit when you mentioned battery re-conditioning. You don't need to pay for that service: You just open up the case; unclip the old ones; replace with the same type.
Assuming that your batteries are OK, your options for increasing speed are:
Add another battery - cost about £30 and will give significantly more speed and power.
Change the sprocket on the wheel to one with lesss teeth- cost £10 to £20, but you need to some spanner work and grinding. It will give about 20% extra speed and a bit more power.
Chuck your batteries and get a 36v lithium one for about £160. A good option if yor present batteries are knackered.
Take off the motor and make some brackets to convert it to a crank drive like Geofft did:
http://www.pedelecs.co.uk/forum/introduce-yourself/12953-hi-warfield-berks.html. You need a free-wheeling crank that cost about £40 or make your own like Geff did.
I don't think buying a kit for £200 plus a new 48v battery is worth it. You might as well buy a new bike. A Bafang BPM kit and a decent 36v battery will cost about £450 from BMSBattery. You can fit it to any bike out of a skip and it'll go as fast as you want and climb any hill.
A lot of these things depend on how good you are at DIY. DIY brings the cost down. You can even make your own batteries out of recycled laptop batteries if you want to put some time in and are capable of understanding electrics. Naturally, the more you pay, the more you get - up to a point. You don't get something for nothing unless you're very lucky.