So a) that's a different paper, b) it's still a 1% fall in absolute terms, c) it's at the optimistic end of most predictions I've seen, and fine, d) here's what the figures look like the -1% a year for 5 years then 2.5%, or 2% in perpetuity:
Bremain Brexit
2017 100 100
2018 102 99
2019 104.04 98.01
2020 106.1208 97.0299
2021 108.243216 96.059601
2022 110.4080803 95.09900499
2023 112.6162419 97.47648011
2024 114.8685668 99.91339212
2025 117.1659381 102.4112269
2026 119.5092569 104.9715076
2027 121.899442 107.5957953
2028 124.3374308 110.2856902
2029 126.8241795 113.0428324
2030 129.360663 115.8689032
2031 131.9478763 118.7656258
2032 134.5868338 121.7347665
2033 137.2785705 124.7781356
2034 140.0241419 127.897589
2035 142.8246248 131.0950287
2036 145.6811173 134.3724045
2037 148.5947396 137.7317146
2038 151.5666344 141.1750074
2039 154.5979671 144.7043826
2040 157.6899264 148.3219922
2041 160.8437249 152.030042
2042 164.0605994 155.830793
2043 167.3418114 159.7265629
2044 170.6886477 163.7197269
2045 174.1024206 167.8127201
2046 177.584469 172.0080381
2047 181.1361584 176.3082391
2048 184.7588816 180.715945
2049 188.4540592 185.2338437
2050 192.2231404 189.8646898
2051 196.0676032 194.611307
2052 199.9889553 199.4765897
2053 203.9887344 204.4635044
Takes until 2053 until we're better off.