Here is an interesting promotion which may offer decent savings if you are willing to be flexible!
As per this web page, British Airways is offering a 15% discount code to shoppers at German department store chain Karstadt. (If you open the page in Chrome, Google will translate it for you.)
The rules are:
Book before 18th October (you can already book now, ignore the 18th September start date)
Travel before 30th April 2014
Travel in short-haul Economy or long-haul World Traveller or World Traveller Plus
Travel must begin from a German destination
The discount is valid on the ENTIRE ticket price, including the taxes
You need to use the promotional code KARSTADT13 on ba.com.
There is not a huge amount of flexibility here to save money on long-haul flights by starting in Germany, as you don’t save enough on World Traveller and World Traveller Plus to justify the trip out there. The exception would be travellers on fully flexible tickets, which are usually cheaper if started outside the UK.
If you have German friends or relatives who were planning a visit to the UK, though, this offers a decent saving.
It may also come in handy if you are flying TO Germany, if you book your trip as two one-way flights. You would then get the discount on the return leg. If you were planning a visit to Frankfurt to fly the new BA A380 on its test flights, this will benefit you as well.