Remember what passport you enter a country determines what nationality you are under there,
If you enter the UK on your Canadian passport you are saying you are Canadian and can call on the embassy in the result of problems.
When you enter Canada on your Canadian passport you cannot call on the British Embassy..
If you are going to the UK to work then entering on your British passport is the logical answer.
I agree it's easiest to enter by showing your British passport, but UK doesn't insist on it (unlike some other countries like US and SA).
It's not true to say that by entering on your Canadian passport, you can request help from the Canadian embassy in case of trouble with authorities. Under international law, the embassy is unable to give assistance to their national when they are also a citizen of the host country, regardless of which passport they present at the border. In fact, when you contact your embassy, high commission or consulate for consular assistance, the first question they ask is 'Are you also a British citizen?', and if you say yes, they will reply, 'Sorry, we cannot assist you in any way,' and ask you to contact relevant UK authorities for help. Of course help will be offered on specific Canadian matters, but not on any problems with UK authorities including the police.
Discretion will be exercised in case of internal unrest, and in the past British embassy has assisted dual British nationals in countries like Algeria at a time of grave civil disorder.