I don't think the UK population is increasing by anything near 2% a year. Worldwide population growth is between 1 and 2% I believe.
I am not definite about a 2% increase for the Witnesses in the UK btw: some of my KMs are missing, but I compared five of the first seven months of the service year and it showed an increase just above 2%.
About pioneers, this appeared in the July KM:
ALL-TIME PEAK: 8,196 regular pioneers reported in March. That is the second all-time peak we have had during 2007. During the last four years there has been a 15-percent increase in the number of regular pioneers in Britain. We commend all who are making room for this priviledge of service.
The next KM shows a new peak of 8,212.
About whether a 2% increase would be 'encouraging', I suppose it depends on your perspective. It would certainly be the best increase the Witness have had in the UK for more than 10 years. On the other hand it does not match the increases JWs had in the 1980s and earlier.
Compared to other religions in the UK where there is almost universal and dramatic decline, it does not look bad at all. In some countries where people are leaving the churches in droves, for the Witnesses even to stand still may be seen as an achievement.
Slim