Print the British Flag!
SpecBAS - 1137 bytes

Absolutely no hope of winning on characters, but the output is in colour...

1 PAPER 15: CLS 
2 PRINT AT 1,2;("_"*42): FOR y=2 TO 42: PRINT AT y,1;"|";AT y,44;"|": NEXT y
3 FOR y=4 TO 18: PRINT AT y,y-2;"\";AT y+1,y-2;"\": NEXT y: PRINT AT 19,17;"\"
4 FOR y=2 TO 14: PRINT AT y,y;"\  \";AT y+28,y+26;"\  \": NEXT y: FOR y=15 TO 17: PRINT AT y,y;"\";AT y+12,y+13;"\": NEXT y
5 FOR y=25 TO 39: PRINT AT y,y+3;"\\": NEXT y: PRINT AT 40,43;"\"
6 FOR y=2 TO 14: PRINT AT y,42-y;"/";AT y+1,42-y;"/": NEXT y: PRINT AT 2,41;"/"
7 FOR y=2 TO 17: PRINT AT y,45-y;"/";AT y+3,45-y;"/": NEXT y
8 FOR y=2 TO 16: PRINT AT y+23,18-y;"/";AT y+26,18-y;"/": NEXT y: PRINT AT 27,17;"/"
9 FOR y=1 TO 13: PRINT AT y+29,17-y;"//": NEXT y: PRINT AT 29,17;"/"
10 PRINT AT 42,18;"__";AT 42,26;"__";AT 42,41;"__"
11 INK 2
12 FOR y=2 TO 42: PRINT AT y,20;"0"*6: NEXT y
13 FOR y=21 TO 23: PRINT AT y,2;"0"*42: NEXT y
14 FOR y=3 TO 18: PRINT AT y,y-1;"0";AT y+23,y+25;"0": NEXT y
15 FOR y=2 TO 16: PRINT AT y,44-y;"0";AT y+26,19-y;"0": NEXT y
16 INK 1
17 FOR y=2 TO 13: LET l$="x"*(14-y): PRINT AT y,4+y;l$;AT y,28;l$;AT 44-y,4+y;l$;AT 44-y,28;l$: NEXT y
18 FOR y=6 TO 19: LET l$="x"*(y-5): PRINT AT y,2;l$;AT y,49-y;l$;AT 44-y,2;l$;AT 44-y,44-LEN l$;l$: NEXT y