I’m afraid that you’re wrong with regard to the procedures around imports from the EU.
Custom and rules of origin declarations - which can be extremely time-consuming and costly to produce - have already been applied to all goods imported from the EU, and the impact of this should in theory already be incorporated into consumer prices. This additional paperwork has undoubtedly contributed to supply chain disruptions and impacted the continuity of the sample taken by the ONS each month when calculating the inflation data (likely a more important point for the RPI than the CPI). But this impact should now be in the price, and the EU has already applied its full range of customs checks on goods exported to the UK, which will again have had an influence on pricing.
As you alluded to, the UK government has however (repeatedly) delayed the remaining physical checks on fresh food produce entering the UK until next year, which will lead to frictions at the border and no doubt have some impact on price. The size of this impact is unclear and given the government’s track record here, it could well turn into a shit show. But I would still argue that the price impact caused by this in Q1-24 may not be significantly larger than the price rises we are still seeing in the first quarter of this year, which is of course the crucial issue for inflation. Also note that many agricultural price indices have fallen significantly over the last few months (20 to 25% declines are commonplace) and the impact of this should reduce consumer food price inflation after the usual lag.
On a broader point, I think people should not confuse the inability of the so-called consensus forecast to correctly anticipate the monthly profile of the CPI with the fundamental forces that will push inflation lower this year (mostly lower energy costs). The Bank of England is particularly bad at forecasting the monthly CPI data, and so a monthly figure which is stronger than expected in the first few months of this year shouldn’t distract from how quickly inflation is likely to fall in H2. I don’t know whether that will disappoint you or not, but falling inflation should impact the polling given how important this issue has become over the past year.