HCS Global.... They have London and Scottish outlets. They make an excellent product that can do voice, Modem & Fax... cost is about UKP120-150. Cheap models can be obtained for a good deal less. RJB Communications (01932) 253 131 has been reported as a cheaper source for these Faxlink devices.
The Lineshare 5000 switch from Lineplex (01483) 211 632, its UKP195 +VAT but very versatile. There are four outputs Phone, TAM, FAX & modem. All the timings can be set, and also can be set to be different depending on whether the switch is set to "IN" or "OUT". It can also recognise that you are "OUT" and changeover to that mode - ditto it can recognise that you are "IN". You can set time windows for IN and OUT, and any of the four outputs can be selected by the caller (old models support just pulse dialling, newer ones two DTMF digits).
In the last few years, a law was passed making documents sent by Fax as legally valid as the original (but I'd still check with your lawyer).