I am planning a trip to Africa and before I book my tickets, I want to make sure of the rules for transporting two rifles through heathrow Airport in London as checked baggage from Toronto to Johannesburg.
A link would be great.

I believe you are OK as long as you don't overnight in London (ie as long as you don't claim your baggage) or as long as you aren't transferring to Gatwick, in which case you have to get a special bonded carrier to transport your guns to Gatwick and check them in for you.

However, don't take this as gospel. I haven't done it personally.

I traveled from Dullas to Heathrow and on to Joberg 2 yrs ago (2004) and on to Windhoek. I never took posession of my guns in the UK and had no problem. On the return trip I had to go thru a bit of red tape in Joberg. On the flight which enters the UK ie Joberg to London you must get permission from the captain to have the guns aboard. This was done in the US going over and I thought it was done in Windhoek but they could not do this since that flight terminated in Joberg. The only problem I had on that trip was the 11 hr layover in Heathrow. You can only walk the terminal so many times.