VPN problems

[#1]

Hi - I work from home 2 days a week.  I connect wirelessly with a Lenovo Thinkpad.  Since the Summer, I have been having serious problems with slow or non-existent connections, with the VPN dropping in and out.  (It connects via Cisco AnyConnect Secure Mobility Client, if that makes any difference).
The problem seems to be only VPN - if I disconnect VPN, I get a good standard internet connection on the Thinkpad - but of course can't connect to my company's network.  I also get a good connection on the family's iMac.
I "only" have standard broadband, but it's been fine until the last couple of months.  I often find that the problem is worse in the afternoons, but quite problematic this morning, which doesn't bode well for this afternoon's work.
My employer's IT department have suggested that Plusnet could be "throttling back on VPN connections" - apparently it is well know that Sky do this, but they had no specific intelligence on Plusnet.  Of course it could be a problem at the company end, but other colleagues who work from home do not have the same issue (none of them are with Plusnet).  Can anyone help please?!

[#2]

Hi mushroompicker,
I've just run some checks and diagnostics on your account and can't see any obvious issues. 
Have you tried turning the Plusnet firewall off? https://portal.plus.net/my.html?action=firewall
Try that first, failing that you might want to take a look around at replies to other similar posts such as this one:
http://community.plus.net/forum/index.php/topic,114286.0.html/