Directly communicated party positions such as in electoral programs or in parliamentary debates do not usually flow unfiltered to citizens. Media emphasizes conflicting and negative issues and in that way affects the transmission of party positions to voters, who perceive a mediated picture of parties. This disconnect is fundamental in representation studies. We propose to focus on mediated party placements as portrayed by journalists in newspapers. For this, we develop a methodological procedure to obtain party positions for fine-grained policy (sub-)issues from newspaper texts in an automated manner combining sentiment analysis with topic models. We focus on the case of territorial politics and its sub-issues in Spain (1976-2019) and in the UK (1900-2018), and make use of news corpora from two mainstream newspaper outlets per case. Our estimates converge to a satisfying degree with expert judgments and manifestos, and show that media alters party self-placements due to its own logic of communication. By comparing positions across newspapers and with parliamentary speeches, we find that aggregation of 20 sentences combined with topic certainty information for sub-issues of interest is ideal to arrive at valid mediated party positions. We describe the position shifting on decentralization of two statewide and two regionalist parties over time in Spain and in the UK, and apply our measurement to a model of party policy shift and regional voter transition. We conclude by discussing the research implications for a new agenda of mediated party positions.