If you remove the upland stations from the minimum temperature list below, then last night there was generally a slight to moderate frost across the country, and not a SEVERE one that has been plastered across the headlines of the forecast for the last couple of days, in fact a good many sites in coastal areas and in eastern England didn't even have an air frost at all.

Mind you, the forecasters build so much scope into their minimum temperature forecasts by having a temperature for towns and cities, and then another one for rural spots, that they are invariably right.

Why not display a colour contoured minimum temperature chart for the whole night and not just at some fixed time, and pick out regional extremes or significant cold spots (as they used to do in the days of magnetic symbols) with a label? The contouring will give most people a clue that temperatures can be lower in valleys or over higher ground.

Here's the subjective frost severity scale out of Wikipedia:

slight frost: 0 to -3.5 °C (32.0 to 25.7 °F)
moderate frost: -3.6 to -6.5 °C (25.6 to 20.3 °F)
severe frost: -6.6 to -11.5 °C (20.2 to 11.3 °F)
very severe frost: below -11.5 °C (11.3 °F)

Lowest Minimum Temperature [18-06]
1800 - 0600 UTC on Saturday, 16 January 2016
In WMO Block 03

[01] 03031 Loch Glascarnoch -9.7 [14.5]
[02] 03044 Altnaharra -8.7 [16.3]
[03] 03047 Tulloch Bridge -8.2 [17.2]
[04] 03041 Aonach Mor. -7.6 [18.3]
[05] 03144 Strathallan -7.4 [18.7]
[06] 03065 Cairngorm -7.2 [19.0]
[07] 03225 Shap -6.8 [19.8]
[08] 03063 Aviemore -6.5 [20.3]
[09] 03507 Sennybridge -6.1 [21.0]
[10] 03162 Eskdalemuir -5.9 [21.4]
[11] 03080 Aboyne -5.4 [22.3]
[12] 03224 Spadeadam -5.3 [22.5]
[13] 03155 Drumalbin -5.1 [22.8]
03226 Warcop -5.1 [22.8]
[14] 03230 Redesdale -4.7 [23.5]
[15] 03529 Pershore -4.1 [24.6]
03220 Carlisle -4.1 [24.6]
[16] 03062 Tain Range -4.0 [24.8]
[17] 03658 RAF Benson -3.7 [25.3]
03039 Bealach Na Ba -3.7 [25.3]
03414 RAF Shawbury -3.7 [25.3]
[18] 03166 Edinburgh Gogarbank -3.6 [25.5]
03971 Mullingar -3.6 [25.5]
[19] 03503 Trawsgoed -3.5 [25.7]
[20] 03148 Glen Ogle -3.4 [25.9]
03136 Prestwick(Royal) -3.4 [25.9]
03212 Keswick -3.4 [25.9]
[21] 03520 Shobdon -3.3 [26.1]
03351 Rostherne -3.3 [26.1]
[22] 03134 Glasgow -3.2 [26.2]
03075 Wick Airport -3.2 [26.2]
03862 Bournemouth -3.2 [26.2]
[23] 03961 Oak Park, Carlow -3.1 [26.4]
03330 Leek Thorncliffe -3.1 [26.4]
[24] 03321 Hawarden -3.0 [26.6]
03970 Claremorris -3.0 [26.6]
03066 RAF Kinloss -3.0 [26.6]
[25] 03853 Yeovilton -2.8 [27.0]
[26] 03132 West Freugh -2.7 [27.1]
03409 Bala -2.7 [27.1]
[27] 03522 Hereford -2.5 [27.5]
[28] 03002 Baltasound -2.3 [27.9]
[29] 03238 Albemarle -2.2 [28.0]
[30] 03967 Casement -2.1 [28.2]
03111 RAF Machrihanish -2.1 [28.2]
03911 Lough Sea -2.1 [28.2]
03171 RAF Leuchars -2.1 [28.2]
[31] 03605 Pembry Sands -2.0 [28.4]
03261 RAF Dishforth -2.0 [28.4]
03318 Blackpool -2.0 [28.4]
03876 Shoreham-by-Sea -2.0 [28.4]
[32] 03301 RAF Mona -1.9 [28.6]
03410 Lake Vyrnwy -1.9 [28.6]
[33] 03034 Aultbea -1.7 [28.9]
03647 Little Rissington -1.7 [28.9]
03740 RAF Lyneham -1.7 [28.9]
03227 Great Dun Fell -1.7 [28.9]
03535 Coleshill -1.7 [28.9]
03966 Gurteen -1.7 [28.9]
[34] 03305 Capel Curig -1.6 [29.1]
03068 RAF Lossiemouth -1.6 [29.1]
03660 High Wycombe -1.6 [29.1]
[35] 03316 Crosby -1.5 [29.3]
03904 Castlederg -1.5 [29.3]
03649 RAF Brize Norton -1.5 [29.3]
03979 Ballyhaise, Cavan -1.5 [29.3]
03344 Bingley -1.5 [29.3]
[36] 03746 Boscombe Down -1.4 [29.5]
[37] 03088 Inverbervie -1.3 [29.7]
03917 Belfast -1.3 [29.7]
03628 Filton -1.3 [29.7]
03346 Leeds -1.3 [29.7]
03158 Charterhall -1.3 [29.7]
03672 RAF Northolt -1.3 [29.7]
[38] 03781 Kenley -1.2 [29.8]
03379 RAF Cranwell -1.2 [29.8]
03210 St Bees Head -1.2 [29.8]
03005 Lerwick -1.2 [29.8]
03839 Exeter Airport -1.2 [29.8]
[39] 03105 Islay -1.1 [30.0]
[40] 03901 Thomastown -1.0 [30.2]
03214 Walney Island -1.0 [30.2]
03749 Middle Wallop -1.0 [30.2]
[41] 03302 RAF Valley -0.9 [30.4]
03313 Rhyl -0.9 [30.4]
03544 Church Lawford -0.9 [30.4]
[42] 03153 Dundrennan -0.8 [30.6]
03882 Herstomonceux West -0.8 [30.6]
03560 Thurleigh -0.8 [30.6]
[43] 03976 Belmullet -0.7 [30.7]
03281 Fylingdales -0.7 [30.7]
[44] 03266 RAF Linton-On-Ouse -0.6 [30.9]
[45] 03915 Portglenone -0.5 [31.1]
03017 Kirkwall -0.5 [31.1]
03743 Larkhill -0.5 [31.1]
03257 RAF Leeming -0.5 [31.1]
03768 Farnborough -0.5 [31.1]
[46] 03969 Dublin -0.4 [31.3]
03761 RAF Odiham -0.4 [31.3]
03680 Rothamsted -0.4 [31.3]
03373 RAF Scampton -0.4 [31.3]
[47] 03204 Isle Of Man -0.3 [31.5]
03710 Liscombe -0.3 [31.5]
03916 Ballypatrick Forest -0.3 [31.5]
[48] 03769 Charlwood -0.2 [31.6]
03354 Nottingham -0.2 [31.6]
03684 Braintree -0.2 [31.6]
[49] 03023 South Uist Range -0.1 [31.8]
[50] 03923 Glenanne 0.0 [32.0]
03590 RAF Wattisham 0.0 [32.0]
03809 Culdrose 0.0 [32.0]
03091 Aberdeen 0.0 [32.0]
03026 Stornoway Airport 0.0 [32.0]