How to wire a light – lighting circuits to be rewired

This week and next we are on a partial rewire. We gave an estimate for the job about 3 months ago and it has taken this long for the job to come up as it is work that the customer is having done through his local council as a grant.

When we gave the estimate for the job we put a disclaimer on it stating that excessive household items be removed from the property for us to be able to do the job.
Well ! as you can see in the picture I have taken of the customers attic, This has not been the case. The house is packed floor to ceiling in every room with boxes and books and newspapers! The customer says he is a collector!
As you can see, even the attic is completely packed with stuff and carpeted and boarded!
We have now suggested another £300 on the estimate and guess what! The customer is saying why? Can we not just go round the edges of the attic to rewire the lighting circuits?
Unfortunately some people have no idea what is involved in a rewire.
Do you think that an extra £300 is ok for having to move and work around all these problems? Bearing in mind it now puts on an extra 2-3 days on the job.