Desktop header bidding in the UK, November 2019 – a market analysis

An analysis into prebid adoption in the UK versus other CEE tested two hypotheses; prebid has a positive impact and is likely to be implemented & UK adoption should be greater than in CEE due to UK market maturity.

The analysis yielded interesting results; prebid is unsurprisingly adopted in the UK (proving hypothesis [1] however to a lesser extent than expected, especially in comparison to Poland. Adoption levels are all round higher in Poland (disproving hypothesis [2]. These findings are tentatively attributed to three suppositions; firstly, the UK market is leaning toward direct deals, secondly, programmatic open auction has greater popularity in Poland, lastly UK’s transition to server-to-server auction.


We have already published a few studies of the header bidding market for PolandBulgaria and Romania and we are not slowing down.

Our November analysis will cover the United Kingdom, one of the biggest programmatic markets in Europe and worldwide. A market estimated to reach $7.59 Billion in programmatic adspend by the end of the year (source Emarketer) & a region that consistently ranks Top 3 in total digital spend after the US & China (source PWC Outlook).

Similar to previous iterations, the hypothesis states that prebid.js-based header bidding has a positive impact on publishers automated sales and therefore they should be likely to implement it.

The secondary hypothesis is to assume that due to the UK markets maturity, prebid.js adoption should be greater than in the regions studied to date (Poland, Bulgaria & Romania).


Using the same proprietary crawler as in previous studies, we scanned desktop websites for ads.txt and prebid.js. We ran it on a list of 1738 domains that we took from the Alexa ranking for the UK.

The list was cleaned in order to make sure that any search engines, social media and corporate websites were not included; we wanted to be 100% sure that the sample was limited to publishers only.

We only took into consideration domains our crawler reported as having implemented ads.txt file. As this IAB standard was created for the sell-side of the advertising market, everything that came without it was automatically filtered out.

The final list included 782 desktop domains. We are aware that there may be some publishers who do not use ads.txt yet, however we believe their number is limited and we wanted to avoid false positives.
Given the maturity of British market, we assume that ads.txt coverage is close to 100%.

The second step was to scan the remaining 782 domains for prebid.js, in order to verify how many of these domains have implemented this header bidding standard. Then we analysed the demand partners included in the prebid.js files and ranked them according to their popularity.

Since Google Ad Manager is not prebid.js compliant, we also scanned websites against direct GAM implementation. The Results can be found below.


45% of the initial 1738 domains contained ads.txt. Leaving 782 domains (henceforth referred to as ‘publisher domains’). This became the scope of the study.


Present in 35% of all 782 publisher domains. & and across 42% of top 156 (top 20% of publisher domains).

Demand Partners/SSPs

Diagram for post


The level of prebid.js adoption in the UK is quite surprising.

35% is less compared to Poland, where it is 46%, but significantly more than in Bulgaria and Romania, where its adoption rate is 18% and 15% respectively.

However, when it comes to the big publishers (top 20%) the level of prebid adoption becomes interesting. The UK & Bulgaria levels are similar. Poland however has a lot higher rate than the other two, notably +33 pp. on the UK.

  • 42% out of top 20% domains in UK
  • 48% of top 20% domains in Bulgaria
  • 75% of top 20% of domains in Poland
  • 17% of top 20% domains in Romania

Diagram for post

While answering the question as to why this is the case would require more in-depth analyses, however we can suppose that:

  • Publishers in the UK rely heavily on strong direct sales or programmatic deals. This is perhaps driven by market pressures on brand safety & quality, as well as generally greater control on programmatic spend; indeed eMarketer suggests that by 2020 PMP spend will overtake open exchange in the UK (source eMarketer).
  • Despite the UK being a more mature market than majority of CEE, Poland seems to be ahead in terms of programmatic, with programmatic open auction enjoying a greater popularity in Poland compared to UK. IAB Europe cited CEE as enjoying a ‘2nd mover advantage’ since 2013, outperforming Western Europe in growth, from 5.5% market share in 2013 to 12.5% in 2018 (source

We can tentatively associate a share of this growth to the prebid adoption rate in Poland and assume that it may be one of the drivers.

  • S2S (server to server) integrations may also play a part in surprising low adoption of prebid in the UK, although reliable information on this is difficult to garner.

The list of most popular demand sources look marginally different compared to CEE.

Noteworthy differences include; the biggest player in the UK is Xandr, not Google & Amazon holds a strong position in the UK, whilst they are barely present in CEE.

Want to know more about header bidding?
E-mail us at [email protected]


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