The "bloke" who you spoke to is a pratt then.
Putting nearly twice the load on the circuit needs changes, ie beefed up wire/relays if not already.
I would start of course by checking fuses, and then the feed between the main light switch and the dip/main stalk, if this carried full load of lights without relays as std, then you are likely to have fried the contacts in the dip/main switch.
Try some Philips Extreme H4 instead when fixed, I used 130/90 and the extreme are slightly brighter!!
Put the dip and main through relays if not already, then you can do a permanent dip mod, ie the dip is turned on with the main light switch, and all the stalk does is turn main on or off, some like it some not, you can see the effect by simply pulling the stalk to the flash position once fixed and driving along on dip at night, as doing this will keep the dip on even on flash/main beam.
tabetha