Confusing or what, the GPO had their own Valve - Thermionic numbering system comprising of a sequence of numbers in range from VT17 to VT207.  Although this alphanumeric code followed the same form as the US Signal Corps one it was quite different.    I have produced a look up table that related GPO VT number with UK CV number and commercial equivalent numbers - a first for the internet I think.  Enjoy:-

VT19 CV1612 VT9B
VT24 CV1636 LS5
VT25 CV1637 LS5
VT26 CV1600 CAT1
VT27 CV1601 CAR1
VT31 CV1638 4101D
VT33 CV1642 DER
VT34 CV1614 ES1500A
VT35 CV1615 ESU1500
VT36 CV1602 CAR4
VT38 CV1645 E133
VT40 CV1647 LS5B
VT46 CV1616 4104A
VT47 CV1603 4104B
VT50 CV1050 HL2K
VT52 CV1025 DET25
VT54 CV1618 ES250M
VT56 CV1648 4205B
VT57 CV25 4242A
VT58 CV1619 4212E
VT60 CV1605 4013C
VT61A CV1609 SW7
VT62 CV1606 CAT2
VT65 CV1649 E133
VT66 CV1650 LS5A
VT68 CV1651 G445
VT69 CV1652 P220A
VT74 CV1654 L2
VT75 CV1655 4019B
VT78 CV1656 LS8
VT82 CV1659 4022B
VT83 CV1660 LS7
VT86 CV1662 P215
VT87 CV1663 4021B
VT88 CV1664 4022AR
VT89 CV1665 DH
VT90 CV1732 ML4
VT91 CV1038 MHL4
VT92 CV1735 DC2/P
VT93 CV1666 P610
VT94 CV1667 LS5X
VT95 CV1668 4033L
VT98 CV1669 P625
VT100 CV1040 PX25
VT105 CV1673 HL2
VT106 CV1674 AC/52PEN
VT107 CV1675 N43
VT109 CV1677 PX25
VT111 CV1679 DA30
VT112 CV1680 PM202
VT114 CV1682 PENA4
VT115 CV1683 MP/PEN
VT119 CV1169 VMP4G
VT120 CV1688 4033L
VT125 CV1689 PA1
VT126 CV1690 9A1
VT127 (CV1187) D41
VT128 CV1692 AC/P
VT131 CV1168 PX4
VT133 CV1695 DDL13
VT136 CV1118 KT2
VT137 CV1081 4052A
VT138 CV1623 RG1-125
VT139 CV399 MH4
VT140 CV1166 LP2
VT143 CV1696 PM2BA
VT144 CV1371 PT6
VT145 CV243 4045A
VT146 CV1625 RG3-250
VT147 CV1697 X41
VT148 CV1698 A819
VT150 CV1699 SP41
VT150A CV1700 SP41
VT151 CV1701 XLO
VT152 CV1702 XP
VT153 CV1703 XW
VT154 CV1067 L63
VT161 CV1710 6C6
VT162 CV1711 6B7
VT163 CV1712 42
VT164 CV1713 EF8
VT167 CV1716 E1541
VT169 CV1717 4307A
VT170 CV1718 AC/TP
VT171 CV1719 U22
VT177 CV1720 XL 1.5
VT178 CV1721 XP 1.5
VT179 CV1722 A901
VT180 CV1053 EF39
VT181 CV1052 EL32
VT182 CV1723 V257
VT183 CV1724 5A/102D
VT185 CV245 4328D
VT188 CV1727 SP210
VT189 CV1128 GT1C
VT190 CV1728 WE262B
VT191 CV1628 GU8
VT193 CV1100 KTW62
VT194 CV587 DH63
VT195 CV1863 5Z4G
VT196 CV509 6V6G
VT199 CV124 807
VT200 CV1065 SP61
VT201 CV1056 EF36
VT202 CV1054 EB34
VT203 CV9 AL60
VT204 CV18 DET19
VT205 CV1630 ESP450
VT207 CV1091 EF50