From personal experience of actually trying to declare commercial items,

1.
Arrived LHR T5
Went as I recall the customs red lane in the south, with several boxes of commercial items. No one there. Just a telephone telling you to ring them. So I did. No answer so after 5 minutes I give up.

Then go up to North customs, still no one there. Use the telephone again, and again no response. Finally, after 10 minutes give up and pass through (items were zero rated for VAT, so was not evading taxes)


Attempt 2
Customs staff actually wondering around baggage reclaim. Presented them with documents, looked at the invoice saw the value and waved me through.


Attempt 3
Went through red lane, this time they took more interest but could not find the right code to calculate duty. Eventually waved me through. Bit odd as I did not have the goods with me as I was connecting to a domestic flight.

As previously stated the OP will be fine. Only those who are breaking the law should fear the law.