1. UK

The Inland revenue provide specific contact details for variou issues on their website. See this page:
http://www.hmrc.gov.uk/contactus/helplines.htm

For VAT, they have a number of specific email addresses:
Belfast - enquiries.ni.bau@hmrc.gsi.gov.uk
Birmingham - enquiries.wm@hmrc.gsi.gov.uk
Cardiff - enquiries.wales@hmrc.gsi.gov.uk
Glasgow - enquiries.sco@hmrc.gsi.gov.uk
Hove - enquiries.se@hmrc.gsi.gov.uk
London - enquiries.lon@hmrc.gsi.gov.uk
Newcastle - enquiries.yhne@hmrc.gsi.gov.uk
North West England - enquiries.nw@hmrc.gsi.gov.uk
Poole - enquiries.estn@hmrc.gsi.gov.uk
Reading - enquiries.sec@hmrc.gsi.gov.uk
Southend-on-Sea - enquiries.estn@hmrc.gsi.gov.uk

2. US

The IRS specify the following numbers:
Live Telephone Assistance - Call 1-800-829-1040
Live Telephone Assistance for Businesses - Call Toll-free, 1-800-829-4933

The email address for their help desk is: helpdesk@speedymail.com