If you’re not bound by an NDA, I’m curious how many channels you have and the monthly cost.
Also, what is your approximate monthly minutes usage (inbound, outbound to fixed, outbound to mobile)?
How many months left on your contract?
During the surge of calls at the beginning and end of the day, approximately what percentage are outgoing?
How are incoming calls handled when staff is unavailable (caller waits in queue, call goes to voicemail, automatic callback, etc.)?
It may make sense to add a secondary provider for outbound calls, especially if your contract allows you to reduce the number of channels with Gamma.
I use https://www.voxbeam.com/ to UK (and many other places) and find their quality and reliability to be excellent. (My account is in USD so the prices and rates below are in $.)
Calls to UK fixed lines are $0.0048/min. (except London $0.0022); mobiles vary by operator but average ~$0.009. Free Phone numbers are free. Billing is per second (no roundup to next minute).
There is no monthly cost for outbound channels, though $1 per channel of your prepaid balance is inaccessible (e.g. if you have 50 channels you have $50 on deposit that you can’t spend, though it would be refunded if you ever cancel the service.)
You can try them at no cost (sign up then open a ticket asking for test credit).
Unfortunately, they don’t offer a suitable metered incoming plan. Incoming channels are quite expensive at $6.60/mo.; DDIs are $0.40/mo., with unlimited minutes and no per minute charges.
Also, take a look at http://www.anveodirect.com/ . UK DDIs are $0.75/mo. + $0.004/min.; get as many channels as needed at no cost. Outbound rates are comparable to Voxbeam, though I’ve no experience calling UK with them.