Yes the fee recently increased to £10. Don't know when exactly, it doesn't seem to have been well publicised.
Just to be clear. You are not making statutory declarations at Yeovil County Court. You are having your SD applications witnessed so that you can submit them to the Traffic Enforcement Centre at Northampton County Court. You can also have them witnessed by a solicitor. They'll charge £5-£10 for each. Some bigger employers have a tame in-house solicitor, they might do it for free for employees.
Once the completed forms are witnessed then you can email them to the TEC, the email address is on the form. Safer than Royal Mail. Scan to PDF or JPEG and attach to the email. I suggest two emails, one for each form. Put something like Statutory Declaration submission attached and the PCN reference number in the subject line. You should get an automatic acknowledgement email from the TEC for each submission.