I can't find the thread, but I think someone recently mentioned upgrading the broadband to get more bandwidth. I don't know where we are contractually with BT, but maybe it's worth switching to another provider such as Be, who are apparently very cheap, fast and reliable.
This is the Be Pro package:https://www.bethere.co.uk/broadbandoffice.do
I rang them and the guy I spoke to said forest would be able to get this on the BT business line and could expect download speeds of 14Mbps. Uploads would be 1.5Mbps. He confirmed the cost would be £21.50 a month in total, with a £24 connection fee. (Last time I checked we pay about £35 a month to BT for broadband)
The only possible complication is that the direct debit may need to be set up via an individual's account rather than the business account, though possibly not.
He said the service is compatible with Linux, though of course they only support Windoze & Mac.