electrical issue

[valvejtw]

hello all, 
1.6 HDI partner 2007
driving along OK when suddenly no dash lights or instruments working,no electric windows,no radio
starts and drives as normal all indicators and external lighting okay, central locking okay radio and window switches light okay
no dash lights or instruments working,no electric windows,no radio
2 days later on a longer run everything started working fine then the next day back to what it was and has been like that since
things tried fuses, earths, wiring, battery condition all good
sent bsi to bba reman for testing no problems with unit 
one thing noticed when I try to operate LH window switch the LH switch dims in brightness the RH window switch dims but not as much
good on the spanners but electrics on this are well beyond my scope (should have kept my 205 could manage the electrics on that) 
any help would be much appreciated 
have had the motor 8 years and would like to keep it another few years only 90000 on clock and its been a one of the best cars I've owned
Jim.