Headlights are juicy things..70W or more so a pair will be 10A plus.
If the fuses are spades, take each one out in turn and look at it -
generally you can see if its blown.
A box of spares of various flavours is not hard to obtain at any garage
or halfords etc.
On a 307 the fuses are one per light, F9, F10, F11, F12 and there are
two relays one for high and one for dipped R5 and R6
That's not likely to be identical, but manufactures tend to do things
mostly te same way in close models, so I am guessing the common element
is one of those relays.
They are no big deal to replace once you identify and can extract the
offending one.
And indeed I have on occasion fixed a relay that was welded over, or
corroded - file the silver contacts with a nail file till bright and clean.
Id expect these to be in the dash area rather than the engine compartment.
OH. here's a fuse chart at least: Looks like F12 (10A) is one suspect -
do reversing lamps work? or F14
http://www.peugeotlogic.com/fuses/fuses306/fuselist7.htm
Also see here
http://www.honestjohn.co.uk/forum/post/index.htm?t=23278