Well, I went grocery shopping earlier today here in the U.S. and I noticed that the isle where they kept candy from the U.K. had shrunk dramatically to practically nothing.
I don't think you have to wait until March to see the effects of a possible no-deal on trade. Stores and other types of businesses outside the U.K. need reliable suppliers for goods and services and I can see why they would start looking elsewhere for goods and services they would normally get from the U.K.
Even with a WA they would probably be reluctant to re-establish trade with the U.K. seeing how things were still quite not settled.
I checked out what the U.K. exports and found this:
" The UKs top ten exports accounted for 74.6 per cent of the overall value of its global shipments in 2013, according to the International Monetary Fund’s World Economic Outlook Database.
Furthermore, exports accounted for 22.7 per cent of total UK economic output.
Pearls, gems, precious metals and coins: £58,544,016,505 (18 per cent of total exports)
Machinery: $70,364,012,000 (13%)
Mineral fuels including oil: £42,316,564,997 (11.5 per cent)
Vehicles excluding trains and streetcars: £29,842,769,695 (9.2 per cent)
Pharmaceutical products: £19,400,359,207 (six per cent)
Electronic equipment: £18,615,930,240 (5.8 per cent)
Optical, technical and medical apparatus: £11,147,461,930 (3.4 per cent)
Aircraft and spacecraft: £10,589,936,289 (3.3 per cent)
Organic chemicals: £7,691,241,858 (2.4 per cent)
Plastics: £7,218,461,794 (2.2 per cent) ".
Companies in these various sectors from outside the U.K if they have any sense at all will be looking for replacement suppliers outside of the U.K.