You are making a very dangerous assesment here Heading Out. Only looking at the trend from the last five months seems wrong to me. Look at what is going on from a year after the peak until now. It could very well be that production increases from some fields in decline for a short while. Could also not be but based on such a short time factor seems quite rigorous.

Then you are as mentioned above also missing the huge buzzard field (200.000 b/d). And 3 small fields each good for around 12.000 b/d (clair in 2005, blane and enoch in 2006).

Then secondly were did the april 2005 decline come from? The data from your link (which is the most reliable UK data source) says this:

January 2005 8,688,739
February 2005 7,729,363
March 2005 7,732,590
April 2005 7,952,636
May 2005 7,413,241

An increase in April?

HO is looking at year-on-year declines in a given calendar month, not month-to-month declines. According to BP Statistical summary, depletion rates where:
99-00: 8.3%
00-01, 7.1%
01-02, 0.5%
02-03, 8.4%
03-04, 10.1%
and the evidence for 04-05 is that it's running closer to 15%. So depletion has been accelerating. I assume the 01-02 anomaly represents a new field ramping up, but I don't know.

You assume in your analysis that depletion before addition of new fields will be 7%, which seems over-optimistic.

Sorry for my mixe-up with year to year and month to month, ill look into it more tomorrow see if i can come up with some predictions and stuff from the industry.