The straight answer is generally 'No' as far as the 'plan' is concerned. The plans are often inaccurate and the Land Registry will actually tell you they are often just an approximation. What they do do is give accurate information of the title, and general information etc. Click on 'Researching Boundaries.
This will help you
http://www.boundary-problems.co.uk/
We are having a battle at the moment with a virtually new neighbour who is using his plans to try and prove we have 'stolen' some of his land (before he bought the property 5 years ago)!! The plans on the land registry site date back to 1969 and the house has seen many new owners since then and the garden areas have changed as people have changed fences etc. The houses are 250 years old. We have been in the house for 30 years and never touched the boundaries. We only had our property registered in 2002 and the neighbours house was registered in 2004 for the first time when he bought it.