diff --git a/.github/workflows/_check.yml b/.github/workflows/_check.yml
deleted file mode 100644
index a6139c19..00000000
--- a/.github/workflows/_check.yml
+++ /dev/null
@@ -1,27 +0,0 @@
-on:
-  workflow_call:
-    outputs:
-      branch-pr:
-        description: The PR number if the branch is in one
-        value: ${{ jobs.pr.outputs.branch-pr }}
-
-jobs:
-  pr:
-    runs-on: "ubuntu-latest"
-    outputs:
-      branch-pr: ${{ steps.script.outputs.result }}
-    steps:
-      - uses: actions/github-script@v7
-        id: script
-        if: github.event_name == 'push'
-        with:
-          script: |
-            const prs = await github.rest.pulls.list({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              head: context.repo.owner + ':${{ github.ref_name }}'
-            })
-            if (prs.data.length) {
-              console.log(`::notice ::Skipping CI on branch push as it is already run in PR #${prs.data[0]["number"]}`)
-              return prs.data[0]["number"]
-            }
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f198a244..223b73ec 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -2,22 +2,19 @@ name: CI
 
 on:
   push:
+    branches:
+      - main
+    tags:
+      - '*'
   pull_request:
 
 jobs:
-  check:
-    uses: ./.github/workflows/_check.yml
-
   lint:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_tox.yml
     with:
       tox: pre-commit
 
   test:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_test.yml
     with:
       python-version: dev
@@ -26,8 +23,6 @@ jobs:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
   docs:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_docs.yml
     permissions:
       contents: write
diff --git a/docs/explanations/decisions/0021-ci-only-pr.md b/docs/explanations/decisions/0021-ci-only-pr.md
new file mode 100644
index 00000000..f5d555be
--- /dev/null
+++ b/docs/explanations/decisions/0021-ci-only-pr.md
@@ -0,0 +1,24 @@
+# 21. Run CI on pull requests and main branch only
+
+Date: 2025-05-06
+
+## Status
+
+Accepted
+
+## Context
+
+CI has been being run on branches that do not have open pull requests, which has: added spurious jobs to the organisation's compute limit; made workflow definitions more complex; made the results page harder to parse; and allowed known working development branches to become stale or forgotten.
+
+Running CI only on branches that have open pull requests will: reduce compute jobs created for code that is known to not be working; simplify workflow definitions; simplify the CI results page; encourage early creation of pull requests, adding visibility to development.
+
+Draft pull requests will still have CI jobs run, ensuring that code quality is maintained while allowing reviewers to ignore changes that are not ready for human review.
+
+## Decision
+
+CI will only be run on all PRs when changes are made, and on the main branch when PRs are merged into it: not on branches that do not have open PRs.
+Opening a draft PR will allow CI to be run, with the understanding that the PR may not be ready for review.
+
+## Consequences
+
+The `check` job will be removed and CI will run on all PRs and on the `main` branch.
diff --git "a/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/_check.yml" "b/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/_check.yml"
deleted file mode 120000
index 9c0f79a5..00000000
--- "a/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/_check.yml"	
+++ /dev/null
@@ -1 +0,0 @@
-../../../.github/workflows/_check.yml
\ No newline at end of file
diff --git "a/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/ci.yml.jinja" "b/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/ci.yml.jinja"
index c00d4217..cf2f0799 100644
--- "a/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/ci.yml.jinja"	
+++ "b/template/{% if git_platform==\"github.com\" %}.github{% endif %}/workflows/ci.yml.jinja"	
@@ -5,19 +5,13 @@ on:
   pull_request:
 
 jobs:
-  check:
-    uses: ./.github/workflows/_check.yml
 
   lint:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_tox.yml
     with:
       tox: pre-commit,type-checking
 {% raw %}
   test:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     strategy:
       matrix:
         runs-on: ["ubuntu-latest"] # can add windows-latest, macos-latest
@@ -35,21 +29,15 @@ jobs:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 {% endraw %}{% if docker %}
   container:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_container.yml
     permissions:
       contents: read
       packages: write
 {% endif %}{% if sphinx %}
   docs:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_docs.yml
 {% endif %}
   dist:
-    needs: check
-    if: needs.check.outputs.branch-pr == ''
     uses: ./.github/workflows/_dist.yml
   {% if pypi %}
   pypi: