You would be better going for something flexible with no tie ins. However Nationwide dont offer these types of products. If you wanted to stay with Nationwide you could take out another fixed and then port it.  However this is a risk as new underwriting will be done for the porting. If they say no you would have to pay the redemption penalty.

 If I were you id go for something with no tie ins. Woolwich have a good life tracker with no fees at the moment. However their service is bad.