The pound sterling (GBP) can be given in change using any number of coins from 1 to 100 except 3 using the standard coins £1, 50p, 20p, 10p, 5p, 2p and 1p. (The two pound coin and five pound coin are irrelevant, and the 25p coin is not seen any more.)
1: £1
2: 2 at 50p
4: 50p, 2 at 20p, 10p
5: 5 at 20p
6 - 10: replace 1 at 20p with 2 at 10p each time
(10: 10 at 10p)
11: 20p, 6 at 10p, 4 at 5p
12: 8 at 10p, 4 at 5p
13 - 20: replace 1 at 10p with 2 at 5p each time
(20: 20 at 5p)
21: 2 at 10p, 14 at 5p, 5 at 2p
22: 1 at 10p, 16 at 5p, 5 at 2p
23: 18 at 5p, 5 at 2p
24 - 44: repeat 21 to 23, but in each group of 3 replace 2 at 5p with 5 at 2p
45: 4 at 5p, 39 at 2p, 2 at 1p
46: 1 at 10p, 45 at 2p
47: 2 at 5p, 45 at 2p
48: 2 at 5p, 44 at 2p, 2 at 1p
49: 2 at 5p, 43 at 2p, 4 at 1p
50: 50 at 2p
51 - 100: replace 1 at 2p with 2 at 1p each time
(100: 100 at 1p)
(Please note that there are probably many other ways of achieving these.)