Can I use sugar instead of malt extract?

I've already started making a 5 gallon batch of bitter, but have just realized that they only put 6 pounds of LME in the kit instead of the 9 pounds that the recipe calls for. I've got a spare 1 pound of DME I can add, should I throw a couple of pounds of sugar in there as well, given I've no way of getting more malt extract today?

You can & it will up the gravity an ABV but it will also dry out your beer - it won't be the same beer but it might be great! With no other choice I'd go ahead , or you can just make a smaller batch.

It would not be the same beer, BUT it will be a do able beer. If you wanted to take a few extra minutes, you can even make it better than using plain WHITE sugar. Take the two pounds of sugar and some water and boil it in a pan til you've made a dark caramel and add that to the boil along with the dme. A lot of bitters use a caramel syrup, like Lyles or dark sugar to achieve some of that caramel depth of flavor.

This would be a good opportunity for some experimentation

Doh! Panic over, I was reading the wrong side of the instructions, and read the 9 lb of grain that would have been required if I wasn't doing extract. Turns out I've got everything I need in the right quantities, the only thing missing is my being smart enough to read the right recipe

By the way, thanks for all the rapid and helpful responses! This is a great forum

FYI, if you do ever get into this situation, you can add additional fermentables (extra extract) after fermentation has started. Just dissolve in water, boil for 10 minutes to drive off O2, cool and add. It will make fermentation last longer.