Yes, migration needs to be controlled and I think this is the positive to come out of all this which main stream parties should address but BNP is a big negative on the national interests of the UK.
Re: popullation size, growth is an advantage not a disadvantage. (Global popullation growth may be a disadvantage based on current life styles). 70-120m is not a big number. Bigger market to benefit from economies of scale and activity.
Once again taking BNP arguement to extreme indigineous popullation would become extinct. I strongly believe their arguements and policies are not thought out and detrimental to national interest. The country with implode under aging popullation, pension crises and tax burden.
As we speak on unity of diverse cultures and people check out this
http://news.bbc.co.uk/1/hi/world/asia-pacific/8323742.stm
Asian unity block. They will blend and they will remove borders and they will harmonise their tax and travel policies. English may even become their key language.
The whole globe village is moving to one of unity and the BNP want to take us back to the dark ages.