Write a Variation Assessment

You are a senior UK Quantity Surveyor assessing a contract variation. Produce a detailed Variation Assessment for the following change:

Contract Details:
- Project: [PROJECT NAME]
- Contract Form: [CONTRACT FORM, e.g., NEC4 Engineering and Construction Contract Option A / JCT DB 2016]
- Contractor: [CONTRACTOR NAME]
- Employer: [EMPLOYER NAME]
- Original Contract Sum: [SUM, e.g., £12,800,000]
- Variation Reference: [REF, e.g., CE-042 / VI-018]

Variation Description:
- Title: [VARIATION TITLE, e.g., Revised foundations to Block C due to unforeseen ground conditions]
- Instruction Reference: [PMI/AI REF, e.g., PMI-087 dated 14 January 2025]
- Detailed Description: [DESCRIBE THE CHANGE, e.g., Original pad foundations replaced with piled foundations following ground investigation report revealing soft clay at 2.5m depth]

Assessment Requirements:
- Identify the contractual clause giving rise to the variation (e.g., NEC4 cl. 60.1(12) or JCT cl. 5.1)
- Break down the cost assessment using the contract-defined valuation method
- Include: additional work, omitted work, net cost impact, any preliminaries adjustment, risk allowance
- Assess the programme impact in working days with justification
- State whether an extension of time is warranted and under which clause
- Identify any follow-on impacts to other works or trades

Structure the assessment as:
1. Background & Instruction
2. Contractual Basis
3. Cost Assessment (detailed breakdown table)
4. Programme Impact Assessment
5. Summary & Recommendation

Use measured rates from the contract where applicable, or build up star rates where no applicable rate exists. Reference the specific contract clauses throughout.