Ask HN: What's the going rate for remote tech support (UK)?

If you call a company for remote tech support what would you expect to pay? (Or, what do you charge if you're on the support end of the call).

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Specific situation - my dad called me for tech support, I remotely controlled 2 computers, analysed the fault [Ad-aware failure to handle Outlook PST files causing outlook to run super slow] and provided a solution. He wants me to charge it to his company. In all the assessment and solution took 3 hours. What should I be charging?