Yes, its on the limit of my knowledge as well, but have a look particularly at Paragraph 58. What this suggests is that Local Authorities would be well-advised not to offer the minimum they think can get away with to homeowners in the first instance because it is likely to draw out the length of the process (and put everyone's costs of employing professional advisors).
I assume from your comments that you have received an initial offer. This will be based on a valuation - I suspect the average of two or three valuations. Valuers are professionals with an expert opinion about the open market price of your house. You also get some financial compensation for inconvenience caused. I'm not sure whether the figures are separately split out for you. Based on this, you consider that you would have to fund another �60k for an equivalent house.
There is room for negotiation on this, but �60k sounds a huge gap. There is a process to follow, and I can't believe you haven't been given an explanation of the appeals route, which ultimately can end up at a Lands Tribunal - a group that has the legal power to determine a value. Is there any more you are able to tell us about how far in this process you have reached?